Coordinated allocation of external memory

ABSTRACT

Methods, devices, and executable instructions are provided for allocating external memory. A request to allocate a portion of memory may be received at a first device. A memory appliance and the first client device are connected by a network. A region of memory of the memory appliance may be allocated as external memory prior to receipt of the request to allocate the portion of memory at the first client device. A subset of the region of memory for the portion of memory allocated may be selected at the first client device and in coordination with a second client device on the network, wherein the portion of memory allocated is external to the first client device and yet is primary memory to the first client device. At least the subset of the region of memory may be mapped at the first client device to a virtual address space.

This application is a continuation application of U.S. Non-provisionalapplication Ser. No. 17/125,542 filed Dec. 17, 2020, which is acontinuation application of U.S. Non-provisional application Ser. No.16/395,329 filed Apr. 26, 2019, which is a divisional of U.S.Non-Provisional patent application Ser. No. 14/854,657, filed Sep. 15,2015, which is a continuation-in-part application of U.S.Non-Provisional patent application Ser. No. 14/530,908, entitled“DYNAMICALLY PROVISIONABLE AND ALLOCATABLE EXTERNAL MEMORY,” filed Nov.3, 2014, which claims priority under 35 USC § 119(e) to, U.S.Provisional Patent Application 62/051,144, “DYNAMICALLY PROVISIONABLEAND ALLOCATABLE EXTERNAL MEMORY” filed Sep. 16, 2014. The entirecontents of each of the above-identified applications are herebyincorporated by reference.

BACKGROUND 1. Field of Invention

This invention relates to storage and retrieval of data in memory, andin particular, to client-side memory access.

2. Background of the Invention

In many computing systems, memory is used to hold programs and data thatare part of a working set of one or more tasks being performed by thesystem. The tasks may be performed in a process and/or a thread. Theworking set of the process and/or the thread may be a set of pages in avirtual address space of the process and/or the thread that arecurrently resident in the memory as opposed to the set of pages in thevirtual address space that are swapped out of the memory. When used forthis purpose, the memory is referred to as primary memory, or mainmemory. In other words, the primary memory may be memory in which theworking sets of the processes executed by the system are stored. Primarymemory is typically associated with a single computer system and isoften physically located inside the computer system or directly attachedto computer system's memory controller. In a non-uniform memory access(NUMA) architecture, the computer system may contain multiple CPU's, andeach CPU may have some primary memory associated with it and/or directlyattached to the CPU's memory controller. Primary memory is oftenarranged in pages, where a page is a unit of access or control supportedby a memory controller. Primary memory is typically comprised of veryfast media, such as random access memory (RAM).

Computing systems also typically have a form of secondary memory, whichis used to hold programs and data that are not part of the working setof the tasks being performed by the system. The programs and data storedin secondary memory may be stored in a file system or be located invirtual memory pages that have been swapped out of primary memory by avirtual memory system. Virtual memory pages may be stored in a swappartition or in a swap file on a file system. Secondary memory may beassociated with one or more computer systems and may be arranged in avariety of ways, such as physically located inside the computer system,directly attached to the CPU bus, attached to a peripheral bus, orconnected to a peripheral via a cable or switched fabric. Secondarymemory is typically comprised of slower media, such as flash memory orspinning disk.

Typically, primary memory media is more expensive than secondary memorymedia. Consequently, computing systems may have larger secondary memorycapacity and a limited primary memory capacity. The limited primarymemory capacity may limit the working set of tasks being performed bythe computing system. Increasing the primary memory capacity of thecomputing system may be prohibitive due to large costs involved.Additionally, the computing system may not have a large number of tasksbeing performed all the time, and therefore, portions of the primarymemory, at times, may not be in use. Thus, large primary memory capacitymay not only be expensive, but also not operational all the time.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments may be better understood with reference to the followingdrawings and description. The components in the figures are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention. Moreover, in the figures,like-referenced numerals designate corresponding parts throughout thedifferent views.

FIG. 1 illustrates a hardware diagram of an example external memorysystem;

FIG. 2 illustrates an example memory appliance;

FIG. 3 illustrates an example client;

FIG. 4 illustrates an example management server;

FIG. 5A and FIG. 5B illustrate an example scenario of a request tomigrate a region;

FIG. 6 illustrates an example external memory allocation system;

FIG. 7 illustrates an example flowchart for creation of an externalmemory allocation;

FIG. 8A illustrates a flow diagram of an example logic of a systemproviding delayed initialization for a region;

FIG. 8B illustrates a flow diagram of an example logic of a systemproviding delayed restore for a region;

FIG. 8C illustrates a flow diagram of an example logic of a systemhandling an I/O fault for delayed initialization and/or delayed restorefor a region;

FIG. 9A illustrates a flow diagram of an example logic of a system usinga registration of on-demand memory for a memory-mapped file;

FIG. 9B illustrates a flow diagram of an example logic of a systemhandling an I/O fault of on-demand memory for a memory-mapped file;

FIG. 10A illustrates a flow diagram of an example logic of a systemhandling a pre-fetch request;

FIG. 10B illustrates a flow diagram of an example logic of a systemhandling a pin request;

FIG. 10C illustrates a flow diagram of an example logic of a systemhandling an unpin request;

FIG. 10D illustrates a flow diagram of an example logic of a systemhandling a reclaim request;

FIG. 11 illustrates a memory architecture diagram of an example systemproviding multiple tiers of memory;

FIG. 12A illustrates a flow diagram of an example logic of a systemperforming batched portion unmap;

FIG. 12B illustrates a flow diagram of an example logic of a systemperforming batched portion invalidation/reclaim;

FIG. 12C illustrates a flow diagram of an example logic of a systemreacting to a pending reclaim operation;

FIG. 13 illustrates a flow diagram of an example logic of a systemproviding point-in-time snapshots with copy-on-write in a page-faulthandler;

FIG. 14 illustrates a flow diagram of an example logic of a systemproviding point-in-time snapshots with copy-on-access in a page-faulthandler.

DETAILED DESCRIPTION

Many protocols are designed to provide on-demand access to data. Forexample, a SCSI over Fibre Channel protocol is designed to allow aprocessor to handle incoming SCSI commands and retrieve the desireddata, such as by reading from disk and/or retrieving the data over anetwork (such as with a Redundant Array of Independent Disks (RAID)array head). Other protocols, such as protocols that support client-sidememory access, are designed to bypass the processor and retrieve thedesired data directly from memory, such as with the Remote Direct MemoryAccess (RDMA) protocol over Infiniband. The latter approach takesadvantage of the latency improvements derived from bypassing theprocessor, but sacrifices the flexibility of being able to use theprocessor to access data that is not included in the memory. Somehardware implementations of memory access protocols supportingclient-side memory access enable the ability to specify portions, suchas pages, of a registered area of memory as not present. Attempts toaccess the portions that are not present using client-side memory accessmay raise an interrupt with the processor, while other attempts toaccess the portions that are present may bypass the processor.

The present disclosure provides technical solutions to one or moretechnical problems relating to on-demand data access of data usingclient-side memory access. For example, the present disclosure providesa technical solution to the technical problem of allowing a system tobegin providing client-side memory access to memory prior to restoringall data in and/or initializing the memory. In another example, thepresent disclosure provides a technical solution to the technicalproblem of presenting a larger region (or more regions) to clients thanfit in the memory of the system. For example, a solution is provided touse client-side memory access to access large amounts of data includedin secondary storage, such as data stored in a hard disk, RAID array,and/or flash storage device. In yet another example, a solution isprovided to organize memories and/or secondary storage with differentattributes into memory tiers.

In still another example, the present disclosure provides a technicalsolution to the technical problem of creating point-in-time snapshots ofa memory region accessible via client-side memory access. The presentdisclosure also provides a solution to the problem of detecting whetherand/or when a portion of a memory region has been accessed and withouthaving to assume that all pages mapped to the communication interfacehave been written to. It would be desirable to avoid needing to makethis assumption. The present disclosure also provides a solution to theproblem of, when using client-side memory access, how to enable to thecommunication interface to retrieve desired data with the processorbecause the communication interface typically processes memory accessoperations without involving the processor of the system.

The present disclosure also provides a technical solution to solve atechnical problem of providing scalable primary memory to a computingsystem. The primary memory may scale on demand. The primary memory maybe external to the computing system. Further, a technical solution isdescribed to solve a technical problem of using available primary memorycapacity optimally. Various other technical problems and theirrespective technical solutions are also provided and will be evident topersons skilled in the art.

For example, it may be beneficial to provide primary memory to a localmachine from an aggregated “pool” of memory, which may be referred to asa ‘memory pool’. The memory pool may be external to the local machine.The memory pool may involve multiple memory appliances, and the memorypool may scale to an infinite or arbitrarily large number of memoryappliances without performance irregularities due to the scaling. Thetechnical solutions described may enable an installation, such as aserver cluster, or an administrator to provision primary memory toservers or persons, associated with the installation, with dynamicpolicies like quotas. Further, the technical solutions described mayenable dynamic allocation of memory by applications from the memory poolon demand, whenever needed. The technical solutions described mayfurther enable primary memory of a local machine, such as a singleserver to balloon to any size needed and shrink back to original sizewhen the larger memory capacity is no longer needed, irrespective of theoriginal memory capacity of the server and substantially without a limiton how large the memory pool may become. Each of the technical solutionsprovided herein may only address one or more of the technical problemsdescribed. Some of the technical solutions apply to client-side memoryaccess to memory that may or may not be external primary memory to theclient. Accordingly, a memory appliance may or may not provide, or becapable of providing, external primary memory to clients.

FIG. 1 illustrates a hardware diagram of an example external memorysystem 100. The external memory system may include a memory appliance110, a management server 120, a client 130, and one or moreinterconnects 140. The external memory system may include more, fewer,or different elements. For example, the external memory system mayinclude multiple clients, multiple memory appliances, and/or multiplemanagement servers. Alternatively, the external memory system mayinclude just the client, just the memory appliance, and/or just themanagement server.

The memory appliance 110 may include memory that may be externallyallocatable as primary memory. Henceforth, throughout this disclosure,unless specified otherwise, “memory” refers to primary memory. Themanagement server 120 may be a memory pool manager, responsible toallocate and/or manipulate memory allocations for the client 130 usingthe memory appliance 110. The client 130 may be a machine or a devicerequesting external memory. The client 130 may contain local memory thatoperates as the primary memory of the client 130. However, the externalmemory allocation may be requested by the client to scale the capacityof the primary memory available locally. Alternatively, or in addition,the client 130 may operate the locally available primary memory as acache memory when accessing the externally allocated memory from thememory appliance 110. For example, cache memory may be used by theclient to reduce average time to access data from the externallyallocated memory. The locally available primary memory may be fasterthan the externally allocated memory and may be used to store copies ofdata from frequently used memory locations of the externally allocatedmemory. For example, the client may read data from or write data to alocation in the externally allocated memory. The client may first checkwhether a copy of the data is in the cache memory, such as the locallyavailable memory. If so, the client may read the data from or write thedata to the cache memory, which may be faster than reading from orwriting to the externally allocated memory.

The memory appliance 110, the management server 120, and the client 130may communicate with each other over the interconnects 140. Thecommunication may be unidirectional or bi-directional. An interconnectmay electrically couple the memory appliance 110, the management server120, and/or the client 130. Each of the interconnects 140 may include aphysical component that transports signals between two or more devices.For example, an interconnect may be a cable, a wire, a parallel bus, aserial bus, a network, a switched fabric, a wireless link, a point topoint network, or any combination of components that transport signalsbetween devices. Alternatively or in addition, the memory appliance 110,the management server 120, and the client 130 may communicate over acommunication network, such as a switched fabric, a Storage Area Network(SAN), an InfiniBand network, a Local Area Network (LAN), a WirelessLocal Area Network (WLAN), a Personal Area Network (PAN), a Wide AreaNetwork (WAN), a circuit switched network, a packet switched network, atelecommunication network or any other now known or later developedcommunication network. The communication network, or simply “network”,may enable a device to communicate with components of other externaldevices, unlike buses that only enable communication with componentswithin and/or plugged into the device itself. Thus, a request forprimary memory made by an application executing on the client 130 may besent over the interconnect 140, such as the network. The request may besent to devices external to the client 130, such as the managementserver 120 and/or the memory appliances 110. In response to the request,the application that made the request may be allocated memory frommemories of one or more memory appliances that are external to theclient 130, instead of being allocated a portion of memory locallyavailable inside the client 130 itself.

The management server 120 may dynamically allocate and/or manipulateexternal memory allocations for the client 130. An external memoryallocation may reference one or more regions in the memory appliance110. The management server 120 may allocate and/or manipulate theregions in the memory appliance 110 using region access logic requests.The client 130 may allocate and/or manipulate external memoryallocations and/or regions using allocation logic requests.

Multiple memory appliances may be “pooled” to create a dynamicallyallocatable, or allocable, external memory pool. For example, new memoryappliances may be discovered, or as they become available, memory of, orwithin, the new memory appliances may be made part of the memory pool.The memory pool may be a logical construct. The memory pool may bemultiple memory appliances known to and/or associated with themanagement server 120. The memory appliances involved in the memory poolmay not know about each other. As additional memory appliances arediscovered, the memory of the memory appliances may be added to thememory pool, in other words, the portions of the memory of the memoryappliances is made available for use by the requesting client 130. Theclient 130 may be able to request dynamically allocatable externalmemory from the memory pool which may be available for use, even thoughthe external memory exists on other machines, unknown to the client 130.The client 130, requesting memory, at time of requesting the memory, maybe unaware of the size of the memory pool or other characteristicsrelated to configuration of the memory pool. The memory pool mayincrease or decrease at any time without a service interruption of anytype to the memory consumers, such as the machines requesting memory.

The external memory allocations may span multiple memory appliances.Thus, the external memory system 100 makes available memory capacity,larger than what may be possible to fit into the requesting client 130,or a single memory appliance 110, or a single server. The memorycapacity made available may be unlimited since any number of memoryappliances may be part of the memory pool. The memory pool may beexpanded based on various conditions being met. For example, themaximally price-performant memory available may be selected to grow thememory pool in a maximally cost-efficient manner. Alternatively, or inaddition, memory appliances may be added at any moment to extend thecapacity and performance of the aggregate pool, irrespective ofcharacteristics of the memory appliances. In contrast, the individualclient 130, such as a server computer, may be limited in physical andlocal memory capacity, and moreover, in order to achieve the largestmemory capacity, expensive memory may have to be used or installed inthe individual client 130 absent dynamically allocatable externalmemory.

Instead, with dynamically allocatable external memory, such as thememory pool, one no longer needs to buy expensive large servers withlarge memory capacity. One may instead buy smaller more energy-efficientand cost-effective servers and extend their memory capacity, on demand,by using dynamically allocatable external memory.

The memory pool may be managed by the management server 120. Themanagement server 120, using various components, may provision externalprimary memory to the client 130 or multiple clients that requestexternal memory allocation. The memory pool manager may provisionexternal memory to different clients at different times according todifferent policies, contracts, service level agreements (SLAs),performance loads, temporary or permanent needs, or any other factors.

For example, the client 130 may be server cluster. By using externalmemory allocation and provisioning, the server cluster need not requireservers to have sufficient pre-existing local memory in order to processall anticipated loads. A typical approach to have each individual serverto have full capacity memory leads to over-purchasing memory for allservers in order to satisfy exceptional cases needed by some servers,some of the time. Instead, with external memory, the server cluster mayprovision portions of external memory where and when needed, therebysaving money, space, and energy, by providing on-demand memory to anycapacity. The server cluster may even support memory capacitiesimpossible to physically fit into a single machine.

In another example, external memory may be dynamically allocatedaccording to performance ratings of the external memory. For example,higher-performance external memory may be provisioned for some purposes,and/or lower-performance, but larger capacity and/or lower cost,external memory for other purposes.

The memory pool may provide dynamic memory allocation so that the client130 may request to receive external memory, and when the external memoryis no longer needed, the client 130 may release the external memory backto the memory pool. The dynamic memory allocation may enable the client130 to allocate a provisioned amount of external memory for variouspurposes on the client 130 at various times, on-the-fly, according toclient-logic needs rather than based on an installation policy, orlocal, internal memory of a particular server.

The client 130 may access the dynamically allocatable external memorythrough a variety of methods. The different methods to access theexternal memory may vary the lowest level addressing used to address theexternal memory. The client 130 may be provided with differentinterfaces for each respective access method. For example, the accessmethods may provide physical mapping, programmatic APIs, or any otherapplication-specific interface, to use the external memory so as tosolve a multitude of diverse problems in optimal ways for every case.The different access methods may even be employed at the same time, andeven against the same external memory allocation.

Depending upon the access method used, external memory operations maynot be constrained to memory page size. For some access methods,external memory operations may be as small as a single byte or characterand scale to any degree.

In an example, the dynamically allocatable external memory may enablemultiple clients to share an external memory allocation. The multipleclients, in this case, may access and/or operate on the data in theshared external memory allocation at the same time. Thus, external andscalable shared memory may be provided to the multiple clientsconcurrently.

As described throughout this disclosure, external memory operations maybe carried out via direct communication, referred to as a client-sidememory access, between the client 130 and the memory appliance 110 thatis part of the memory pool. The client-side memory access provides aconsistent low latency, such as 2 micro-seconds. The client-side memoryaccess also provides determinacy, or in other words a predictableperformance, such as a determinate amount of time for a given memoryoperation to be performed. Thus, by using the client-side memory access,the dynamically allocatable external memory provides a high level ofdeterminacy and consistent performance scaling even as more memoryappliances and external memory clients are deployed and/or used fordynamic load balancing, aggregation, and/or re-aggregation.

Dynamically allocatable external memory may also be persistent, meaningthe data stored in the external memory is durable over time. Thisextends the memory paradigm to include the persistence aspects ofexternal storage while retaining the performance of memory. Thisprovides performance of memory with conveniences of a storage paradigm.

FIG. 2 illustrates the example memory appliance 110. By way of example,the system 100 for dynamically allocatable external memory may storedata of one or more regions in one or more memory appliances. The memoryappliance 110 may be a server, a device, an embedded system, a circuit,a chipset, an integrated circuit, a field programmable gate array(FPGA), an application-specific integrated circuit, a virtual machine,an operating system, a kernel, a device driver, a device firmware, ahypervisor service, a cloud computing interface, and/or any otherhardware, software, and/or firmware entity which may perform the samefunctions as described. The memory appliance 110 may include a memory210, a memory controller 220, a communication interface 230, a processor240, a storage controller 250, and a backing store 260. In otherexamples, the memory appliance may contain different elements. Forexample, in another example, the memory appliance 110 may not includethe storage controller 250 and the backing store 260. The memory 210 mayfurther include a region access logic 212, one or more regions 214,region metadata 215, and an observer logic 218. The observer logic 218may not be present in other example memory 210. The region access logic212 and/or the observer logic 218 may be referred to as a region accessunit and/or a observer unit respectively. The memory appliance mayinclude more, fewer, or different elements. For example, the memoryappliance 110 may include multiple backing stores, multiple storagecontrollers, multiple memories, multiple memory controllers, multipleprocessors, or any combination thereof. The memory appliance 110 maystore data received over the one or more interconnects 140.

The region access logic 212 in the memory appliance 110 may register theregions 214 or portions of the regions with one or more communicationinterfaces 230. Alternatively, or in addition, the region access logic212 may provide and/or control access to the region 214 by one or moreclients and/or one or more management servers. A communication interfacein the client 130 may provide client-side memory access to the memory210 of the memory appliance 110, to the regions 214, and/or to portionsof the regions in the memory appliance 110. One or more interconnects ornetworks may transport data between the communication interface of theclient 130 and the communication interface 230 of the memory appliance110. For example, the communication interfaces may be network interfacecontrollers or host controller adaptors.

A client-side memory access may bypass a processor, such as a CPU(Central Processing Unit), at the client 130 and/or may otherwisefacilitate the client 130 accessing the memory 210 on the memoryappliance 110 without waiting for an action by the processor included inthe client 130, in the memory appliance, or both. For example, theclient-side memory access may be based on the Remote Direct MemoryAccess (RDMA) protocol. The RDMA protocol may be carried over an InfiniBand interconnect, an iWARP interconnect, an RDMA over Converged Ethernet(RoCE) interconnect, and/or any other interconnect and/or combination ofinterconnects known now or later discovered. Alternatively, or inaddition, the client-side memory access may be based on any otherprotocol and/or interconnect that may be used for accessing memory. Aprotocol that may be used for accessing memory may be a CPUprotocol/interconnect, such as HyperTransport and/or Quick PathInterconnect (QPI). Alternatively, or in addition, a protocol that maybe used for accessing memory may be a peripheral protocol/interconnect,such as Peripheral Component Interconnect (PCI), PCI Express, PCI-X,ISA, and/or any other protocol/interconnect used to interface withperipherals and/or access memory. The communication interfaces mayprovide reliable delivery of messages and/or reliable execution ofmemory access operations, such as any memory access operation carriedout when performing the client-side memory access. Alternatively, or inaddition, delivery of messages and/or execution of memory accessoperations may be unreliable, such as when data is transported betweenthe communication interfaces using the User Datagram Protocol (UDP). Theclient 130 may read, write, and/or perform other operations on thememory 210, to the regions 214 within the memory 210, and/or to portionsof the regions using client-side memory access. In providing client-sidememory access, the client 130 may transmit requests to perform memoryaccess operations to the memory appliance 110. In response, the memoryappliance 110 may perform the memory access operations. Similar to asdone by the storage device of U.S. patent application Ser. No.13/036,544, filed Feb. 28, 2011, entitled “High performance data storageusing observable client-side memory access” by Stabrawa, et al., whichpublished as US Patent Application Publication US2012/0221803 A1, andwhich is hereby incorporated by reference, the memory appliance 110 mayobserve or otherwise identify the memory access operations. In responseto identifying the memory access operations, the memory appliance 110may, for example, copy the data of the region 214 to one or more backingstores 260 independently of performing the memory access operations onthe memory 210. A backing store 260 may include one or more persistentnon-volatile storage media, such as flash memory, phase change memory,memristors, EEPROM, magnetic disk, tape, or some other media. The memory210 and/or the backing store 260 (if included) may be subdivided intoregions.

The memory appliance may be powered by a single power source, or bymultiple power sources. Examples of the power source include a publicutility, internal or external battery, an Uninterruptible Power Supply(UPS), a facility UPS, a generator, a solar panel, any other powersource, or a combination of power sources. The memory appliance maydetect the condition of the one or more power sources that power thestorage device.

The memory 210 may be any memory or combination of memories, such as asolid state memory, a random access memory (RAM), a dynamic randomaccess memory (DRAM), a static random access memory (SRAM), a flashmemory, a read-only memory (ROM), an electrically erasable programmableread-only memory (EEPROM), a flash memory, a phase change memory, amemristor memory, any type of memory configured in an address spaceaddressable by the processor, or any combination thereof. The memory 210may be volatile or non-volatile, or a combination of both.

The memory 210 may be a solid state memory. Solid state memory mayinclude a device, or a combination of devices, that stores data, isconstructed primarily from electrical conductors, semiconductors andinsulators, and is considered not to have any moving mechanical parts.Solid state memory may be byte-addressable, word-addressable orblock-addressable. For example, most dynamic RAM and some flash RAM maybe byte-addressable or word-addressable. Flash RAM and other persistenttypes of RAM may be block-addressable. Solid state memory may bedesigned to connect to a memory controller, such as the memorycontroller 220 in the memory appliance 110, via an interconnect bus 270,such as the interconnect 270 in the memory appliance 110.

Solid state memory may include random access memory that permits storeddata to be read and/or written in any order (for example, at random).The term “random” refers to the fact that any piece of data may bereturned and/or written within a constant time period, regardless of thephysical location of the data and regardless of whether the data isrelated to a previously read or written piece of data. In contrast,storage devices such as magnetic or optical discs rely on the physicalmovement of the recording medium or a read/write head so that retrievaltime varies based on the physical location of the next item read andwrite time varies based on the physical location of the next itemwritten. Examples of solid state memory include, but are not limited to:DRAM, SRAM, NAND flash RAM, NOR flash RAM, phase change memory (PRAM),EEPROM, FeRAM, MRAM, CBRAM, PRAM, SONOS, RRAM, Racetrack memory, NRAM,Millipede, TRAM, Z-Ram, and TTRAM.

In contrast to solid state memory, solid state storage devices aresystems or devices that package solid state memory with a specializedstorage controller through which the packaged solid state memory may beaccessed using a hardware interconnect that conforms to a standardizedstorage hardware interface. For example, solid state storage devicesinclude, but are not limited to: flash memory drives that include SerialAdvanced Technology Attachment (SATA) or Small Computer System Interface(SCSI) interfaces, Flash or DRAM drives that include SCSI over FibreChannel interfaces, DRAM drives that include SATA or SCSI interfaces,and USB (universal serial bus) flash drives with USB interfaces.

The memory 210 may include the region access logic 212, the region 214,and the region metadata 215. In an example, each portion of the memory210 that includes a corresponding one of the region access logic 212,the region 214, and the region metadata 215 may be of a different typethan the other portions of the memory 210. For example, the memory 210may include a ROM and a solid state memory, where the ROM includes theregion access logic 212, and the solid state memory includes the region214 and the region metadata 215. The memory 210 may be controlled by thememory controller 220. The memory 210 may include more, fewer, ordifferent components. For example, the memory may include the observerlogic 218.

The processor 240 may be a general processor, a central processing unit(CPU), a server, a microcontroller, an application specific integratedcircuit (ASIC), a digital signal processor, a field programmable gatearray (FPGA), a digital circuit, an analog circuit, or any combinationthereof. The processor 240 may include one or more devices operable toexecute computer executable instructions or computer code embodied inthe memory 210 or in other memory to perform features of the externalmemory system. For example, the processor 240 may execute computerexecutable instructions that are included in the observer logic 218 andthe region access logic 212.

The processor 240, the memory controller 220, and the one or morecommunication interfaces 230 may each be in communication with eachother. Each one of the processor 240, the memory controller 220, and theone or more communication interfaces 230 may also be in communicationwith additional components, such as the storage controller 250, and thebacking store 260. The communication between the components of thememory appliance 110 may be over an interconnect, a bus, apoint-to-point connection, a switched fabric, a network, any other typeof interconnect, or any combination of interconnects 270. Thecommunication may use any type of topology, including but not limited toa star, a mesh, a hypercube, a ring, a torus, or any other type oftopology known now or later discovered. Alternatively or in addition,any of the processor 240, the memory 210, the memory controller 220,and/or the communication interface 230 may be logically or physicallycombined with each other or with other components, such as with thestorage controller 250, and/or the backing store 260.

The memory controller 220 may include a hardware component thattranslates memory addresses specified by the processor 240 into theappropriate signaling to access corresponding locations in the memory210. The processor 240 may specify the address on the interconnect 270.The processor 240, the interconnect 270, and the memory 210 may bedirectly or indirectly coupled to a common circuit board, such as amotherboard. In one example, the interconnect 270 may include an addressbus that is used to specify a physical address, where the address busincludes a series of lines connecting two or more components. The memorycontroller 220 may, for example, also perform background processingtasks, such as periodically refreshing the contents of the memory 210.In one example implementation, the memory controller 220 may be includedin the processor 240.

The one or more communication interfaces 230 may include any one or morephysical interconnects used for data transfer. In particular, the one ormore communication interfaces 230 may facilitate communication betweenthe memory appliance 110 and the client 130, between the memoryappliance 110 and the management server 120, between the memoryappliance 110 and any other device, and/or between the management server120 and any other device. The one or more communication interfaces 230may communicate via the one or more interconnects. The one or morecommunication interfaces 230 may include a hardware component. Inaddition, the one or more communication interfaces 230 may include asoftware component. Examples of the communication interface include aDirect Memory Access (DMA) controller, an RDMA controller, a NetworkInterface Controller (NIC), an Ethernet controller, a Fibre Channelinterface, an InfiniB and interface, a SATA interface, a SCSI interface,a USB interface, an Ethernet interface, or any other physicalcommunication interface. The one or more communication interfaces 230may facilitate client-side memory access, as described throughout thisdisclosure.

The region 214 may be a configured area of the memory 210 that isaccessible via a memory access protocol and/or storage protocol nowknown or later discovered. Storage protocols and memory access protocolsare described elsewhere in this disclosure. The region 214 may be alogical region which maps a sequence of data blocks to correspondingmemory locations in the memory 210. Therefore, in addition to the datablocks themselves, the region 214 may include region information, suchas a mapping of data blocks to memory locations or any other informationabout the data blocks. The data blocks of the region 214, which may beconfigured by the region access logic 212, may all be stored in thememory 210. The volume information may or may not be included in thememory 210. Accordingly, when the region 214 is said to be included inthe memory 210, at least the data blocks of the region 214 (the datastored in the region) are included in the memory 210. Alternatively, orin addition, the volume information may be included in the regionmetadata 215.

The region metadata 215 may include properties, configurationparameters, and/or access parameters related to the region 214.

Properties may include the size of the region, references to portionswithin the memory allocated to the region 214, and/or any other aspectsdescribing the region 214, its data, its memory, and/or its backingstore.

Configuration parameters may include an indication of whether or not theregion 214 may be persisted to the backing store 260, an indication ofwhat method may be used to persist the region 214 to the backing store260, an identifier which may be used to locate persisted data related tothe region 214, and/or any other parameters used to specify how theregion 214 may behave or be treated.

Access parameters may include a list of zero or more communicationinterfaces 230 included in the memory appliance 110 which may be used toaccess the region 214, a list of zero or more clients, memoryappliances, and/or management servers which are allowed to access theregion 214, a list of zero or more communication interfaces of clients,memory appliances, and/or management servers which are allowed to accessthe region 214, a password which may be used to authenticate access tothe region 214, an encryption key which may be used to authenticateaccess to the region 214, access permissions, and/or any otherparameters used to specify how the region may be accessed.

Access permissions may include a mapping of access method to permissionsgranted and/or revoked. Access methods may include: via a specifiedcommunication interface 230 included in the memory appliance 110; via aspecified communication interface of a client, memory appliance, and/ormanagement server; by a specified client; by a specified memoryappliance; by a specified management server; using a specified password;using a specified encryption key; and/or any other identifiable methodused to access the region.

Permissions may include data read access, data write access, metadataread access, metadata write access, destroy access, and/or any othercapability that may be selectively granted and/or revoked to a client, amemory appliance, and/or a management server. For example, the accessparameters may include access permissions that indicate that aparticular management server may read the metadata for the region 214,but may not read and/or write the data of the region 214. In a secondexample, the access parameters may include access permissions thatindicate that a particular client may read the data for the region 214,but may not write the data for the region 214.

The storage controller 250 of the memory appliance 110, of themanagement server 120, and/or of the client 130 may include a componentthat facilitates storage operations to be performed on the backing store260. A storage operation may include reading from or writing tolocations within the backing store 260. The storage controller 250 mayinclude a hardware component. Alternatively or in addition, the storagecontroller 250 may include a software component.

The backing store 260 of the memory appliance 110, of the managementserver 120, and/or of the client 130 may include an area of storagecomprising one or more persistent media, including but not limited toflash memory, phase change memory, Memristors, EEPROM, magnetic disk,tape, or other media. The media in the backing store 260 may potentiallybe slower than the memory 210 on which the region 214 is stored.

The storage controller 250 and/or backing store 260 of the memoryappliance 110 may be internal to the memory appliance 110, a physicallydiscrete component external to the memory appliance 110 and coupled tothe backing store 260, included in a second memory appliance or in adevice different from the memory appliance 110, included in themanagement server 120, included in the client 130, part of a server,part of a backup device, part of a storage device on a Storage AreaNetwork, and/or part of some other externally attached persistentstorage. Alternatively, or in addition, a region included in a differentmemory appliance may be used as the backing store for the memoryappliance 110.

FIG. 3 illustrates the example client 130. The client 130 may include amemory 310, a memory controller 320, a processor 340, and acommunication interface 330, similar to the memory 210, the processor240, the communication interface 230, and the memory controller 220 ofthe memory appliance 110. The client 130 may include more, fewer, ordifferent components. For example, the client 130 may include a storagecontroller 350, a backing store 360, multiple storage controllers,multiple backing stores, multiple memories, multiple memory controllers,multiple processors, or any combination thereof. Alternatively, theclient 130 may just include a process executed by the processor 340.

The storage controller 350 and/or backing store 360 of the client 130may be internal to the client 130, a physically discrete device externalto the client 130 that is coupled to the client 130, included in asecond client or in a device different from the client 130, included inthe management server 120, included in the memory appliance 110, part ofa server, part of a backup device, part of a storage device on a StorageArea Network, and/or part of some other externally attached persistentstorage. Alternatively, or in addition, the region 214 included in thememory appliance 110 may be used as the backing store 360 for the client130.

The memory 310 of the client 130 may include a client logic 312. Thememory 310 of the client 130 may include more, fewer, or differentcomponents. For example, the memory 310 of the client 130 may include anapplication logic 314, the region metadata 215, a data interface 316,and/or external memory allocation metadata 318. The processor 340 mayexecute computer executable instructions that are included in the clientlogic 312 and/or the application logic 314. Alternatively, or inaddition the client logic 312, the application logic 314, and/or thedata interface 316 may be referred to as a client logic unit 312, anapplication logic unit 314 and/or a data interface unit, respectively.The components of the client 130 may be in communication with each otherover an interconnect 370, similar to the interconnect 270 in the memoryappliance 110 or over any other type of interconnect.

The application logic 314 may include a user application, an operatingsystem, a kernel, a device driver, a device firmware, a virtual machine,a hypervisor, a container, a jail, a cloud computing interface, acircuit, a logical operating system partition, or any other logic thatuses the services provided by the client logic 312. The applicationlogic 314 may be embedded in a chipset, an FPGA, an ASIC, a processor,or any other hardware device.

FIG. 4 illustrates the example management server 120. The managementserver 120 may include a memory 410, a processor 440, a communicationinterface 430, and a memory controller 420, similar to the memory 210,the processor 240, the communication interface 230, and the memorycontroller 220 of the memory appliance 110. The management server 120may include more, fewer, or different components. For example, themanagement server may include a storage controller 450, a backing store460, multiple storage controllers, multiple backing stores, multiplememories, multiple memory controllers, multiple processors, or anycombination thereof. Alternatively, the management server 120 may justinclude a process executed by the processor 440.

The storage controller 450 and/or backing store 460 of the managementserver 120 may be internal to the management server 120, a physicallydiscrete device external to the management server 120 that is coupled tothe management server 120, included in a second management server or ina device different from the management server 120, included in theclient 130, included in the memory appliance 110, part of a server, partof a backup device, part of a storage device on a Storage Area Network,and/or part of some other externally attached persistent storage.Alternatively, or in addition, the region 214 included in the memoryappliance 110 may be used as the backing store 460 for the managementserver 120.

The memory 410 of the management server 120 may include an allocationlogic 412 and/or external memory allocation metadata 414. The memory 410of the management server 120 may include more, fewer, or differentcomponents. For example, the memory 410 of the management server 120 mayinclude region metadata 215. The processor 440 may execute computerexecutable instructions that are included in the allocation logic 412.The allocation logic 412 may be referred to as an allocation logic unit.The components of the management server 120 may be in communication witheach other over an interconnect 470, such as the interconnect 270 in thememory appliance 110 or over any other type of interconnect.

During operation of the external memory system, the region access logic212 may provide the client 130 and/or management server 120 withclient-side memory access to the region 214. Alternatively, or inaddition, the region access logic 212 may provide other memoryappliances with client-side memory access to the region 214. Client-sidememory access may include a memory access operation. A memory accessoperation may include, for example, a read memory operation or a writememory operation. The memory access operation may be performed by thememory appliance 110 in response to receiving a request from the client130 and/or management server 120 at the communication interface 230 ofthe memory appliance 110. The request may include, for example, astarting memory offset, a size of memory allocation, a starting memorylocation, a number of units of memory to access, or any other attributerelating to the requested memory access operation. The request mayaddress the memory 210 on a block-addressable basis, a word-addressablebasis, a byte-addressable basis, or on any other suitable unit of memorybasis.

The region access logic 212 may register the region 214 with thecommunication interface 230 and/or with a device other than the memoryappliance, such as with the client 130 and/or management server 120.Alternatively or in addition, the region access logic 212 may determinea location or locations in the memory 210 of the memory appliance 110where the region 214 is located. The region access logic 212 mayregister the location or locations with the communication interface 230and/or with a device other than the memory appliance 110, such as withthe client 130 and/or management server 120.

The region access logic 212 may control and/or specify how the region214 may be accessed. For example, the region access logic 212 maycontrol which regions are available on the memory appliance 110 and/orwhich operations may be performed. In one example, the region accesslogic 212 may control access based upon the current time, day, month oryear; an identity or a location of the communication interface, anidentity or a location of the client and/or management server; or someother attribute of the client 130, the memory appliance 110, themanagement server 120, the interconnect 140, or of the surroundingenvironment that is detectable by the region access logic 212, such asthe condition of the power source that powers the memory appliance 110.Alternatively or in addition, the region access logic 212 may controlaccess based on an authentication mechanism, including but not limitedto a password, a key, biometrics, or a cryptographic authentication.

The region access logic 212 or the communication interface 230 mayprovide client-side memory access using any memory access protocol nowknown or later discovered. The memory access protocol may be anycommunication protocol used to transfer data between a memory in a firstdevice, such as the memory 310 in the client 130, and a memory in asecond device, such as the memory 210 in the memory appliance 110, wherethe data is transferred independently of CPU's in the first and seconddevices, such as the processor 340 in the client 130 and the processor240 in the memory appliance 110. Therefore, in examples where the firstdevice includes an operating system, the data may be transferred fromthe memory of the first device to the memory of the second devicewithout involvement of the operating system. Although instructionsexecuted by the CPU may direct a hardware data controller to transferthe data from the memory of the first device to the memory of the seconddevice, the actual transfer of the data between the memories may becompleted without involvement of the CPU and, if the first deviceincludes an operating system, without involvement of the operatingsystem. The memory access protocol may describe, for example, a formatof the request for the memory access operation to be performed on thememory in the second device or system.

The memory access protocol may be implemented, for example, using one ormore hardware controllers, such as the communication interface 230 inthe memory appliance 110 and the communication interface 330 in theclient 130. The memory access protocol and electrical characteristics ofthe hardware controller may be part of a common standard. Accordingly,the memory access protocol and electrical characteristics of thecommunication interfaces may be part of one standard. In one example,the access protocol may be the RDMA protocol implemented in thecommunication interfaces, where the memory access protocol and thecommunication interfaces conform to an InfiniBand standard. In a secondexample, the memory access protocol may be Internet Wide Area RDMAProtocol (iWARP), where iWARP is implemented in the communicationinterfaces, and where the communication interfaces conform to an iWARPstandard. The iWARP standard, which is an Internet Engineering TaskForce (IETF) protocol, is RDMA over TCP (Transport Control Protocol). Ina third example, the memory access protocol may be RDMA over ConvergedEthernet (RoCE), where RoCE is implemented in the communicationinterfaces, and where the communication interfaces conform to RoCE andEthernet standards. In a third example, the memory access protocol maybe a PCI bus-mastering protocol implemented in the communicationinterfaces, where the communication interfaces conform to a PCIstandard. The memory access protocol, such as RDMA, may be layereddirectly over a transport protocol, such as TCP.

The region access logic 212, the client logic 312, and/or the allocationlogic 412 may utilize multiple communication interfaces to provideresiliency against various communication failure modes. Communicationfailure modes may include failure of one or more communicationinterfaces, failure of one or more ports included in one or morecommunication interfaces, failure of a portion of the interconnect, suchas an interconnect cable or interconnection fabric switch, and/or anyother failure that may sever a network link between any twocommunication interfaces. The region access logic 212 may provideresiliency against communication failure modes using features of thecommunication interfaces. In a first example, the region access logic212 may configure the communication interfaces to use an alternate pathif a primary path experiences interconnect errors, such as usingInfiniBand Automatic Path Migration. In a second example, the regionaccess logic 212 may provide resiliency against communication failuremodes by choosing communication modes that are by design resilientagainst interconnect errors, such as InfiniBand reliable connections,TCP connections, etc. Alternatively, or in addition, the region accesslogic 212 may provide resiliency against communication failure modes byestablishing multiple active network links, and using one or more of thenon-failing network links to provide connectivity. The multiple activenetwork links may be selected to optimize redundancy versus failures.For example, the multiple network links may utilize different ports ondifferent communication interfaces, such that a failure of one port orone communication interface may only cause one of the multiple activenetwork links to fail.

In one or more examples, the region access logic 212 may additionallyprovide block-level access to the region 214 using any storage protocolnow known or later discovered. A storage protocol may be anycommunications protocol used to transfer data between a block storagedevice or system, such as the memory appliance 110, and a device orsystem, such as the client 130, that stores data in, and/or retrievesdata from, the block storage device or system. A storage protocol may beimplemented, for example, using one or more software and/or hardwarestorage controllers. The storage protocol and electrical characteristicsof the hardware storage controller may be part of a common standard. Inone example, the storage protocol may be the universal serial bus massstorage device class (USB MSC or UMS), which is a set of computingcommunications protocols defined by the USB Implementers Forum that runson a hardware bus, such as the interconnect, that conforms to the USBstandard. In a second example, the storage protocol may be the SCSIcommand protocol. In a third example, the storage protocol may be theSATA protocol. Additional examples of the storage protocol includeSerial Attached SCSI (SAS) and Internet Small Computer System Interface(iSCSI). Alternatively or in addition, the region access logic 212 mayprovide block-level access using any storage protocol that transfersdata with a data transfer protocol, such as SCSI over Fibre Channel,SCSI RDMA Protocol (SRP) over Remote Direct Memory Access (RDMA), iSCSIover TCP/IP, or any other combination of storage protocol and datatransfer protocol known now or discovered in the future.

Accessing the region 214 using the storage protocol may be slower thanaccessing the region 214 using the memory access protocol. In contrastto the memory access protocol, the processor 340 of the client 130 mayinteract with the storage controller 350 during the transfer of data tothe block storage device 360 or system, where the storage controllerimplements the storage protocol. Therefore, the storage protocol isdifferent from the memory access protocol.

By providing block-addressable client-side memory access and/orblock-level access through the region access logic 212, the memoryappliance 110 may be considered, in an example implementation, a blockstorage device. A block storage device may also be referred to as ablock device. A block device stores data in blocks of a predeterminedsize, such as 512 or 1024 bytes. The predetermined size may beconfigurable. A block device is accessed via a software and/or hardwarestorage controller and/or a communication interface, such as thecommunication interface 230. Examples of other block devices include adisk drive having a spinning disk, a tape drive, a floppy disk drive,and a USB flash pen drive.

The region access logic 212 may subdivide the memory 210, and/or thebacking store 260 into one or more regions. Each one of the regions,such as the region 214 in the memory 210 of the memory appliance 110,may be a configured area of storage that is accessible via any accessprotocol and/or storage protocol. Access protocols and storage protocolsare described elsewhere in this disclosure.

The backing store 260 may include any block device. Examples of blockdevices include, but are not limited to, hard disks, CD-ROM drives, tapedrives, solid state storage devices, flash drives, or any other massstorage device.

The client logic 312 and/or the allocation logic 412 may perform memoryaccess operations on the region 214 in the memory 210 of the memoryappliance 110 using client-side memory access over the memory accessprotocol. Alternatively or in addition, the client logic 312 and/or theallocation logic 412 may perform operations to discover the memoryappliance 110 when connected, or to discover available regions that maybe accessible on the memory appliance 110. Alternatively or in addition,the client logic 312 and/or the allocation logic 412 may performadministration operations to modify attributes or metadata, such as theregion metadata 215, associated with the region 214. The operations mayinclude sending region access logic requests, described elsewhere inthis disclosure. In an example, the client logic 312 and/or theallocation logic 412 may perform an administration operation to set ahuman readable label associated with the region 214. In an example, theclient logic 312 and/or the allocation logic 412 may perform anadministration operation to change the operations that are available tothe client 130 and/or to other clients. The administration operationsmay be used, for example, to coordinate shared access to the region bymultiple clients.

The client logic 312 and/or the allocation logic 412 may performoperations that communicate information to the observer logic 218 abouta set of one or more memory access operations that were requested orthat are to be requested by the client logic 312 and/or the allocationlogic 412. For example, the client logic 312 and/or the allocation logic412 may transmit a notification message via the communication interface330 of the client 130 and/or the communication interface 430 of themanagement server 120. The observer logic 218 may receive thenotification message via the communication interface 230 of the memoryappliance 110. The notification message may precede or follow the set ofmemory access operations requested by the client logic 312 and/or theallocation logic 412. The notification message may identify attributesof the set of memory access operations.

Alternatively or in addition, the client logic 312 and/or the allocationlogic 412 may perform memory access operations that are directlyobservable or identified by the observer logic 218. For example, therequest to perform the memory access operation may include notificationinformation, such as an RDMA write with immediate value operation. Inaddition to writing to the memory in the region 214, the write withimmediate value operation may cause the observer logic 218 to receive anotification that includes the immediate value specified by the clientlogic 312 and/or the allocation logic 412 in the RDMA write withimmediate value operation. The value may include one or more attributesof the memory access operation. For example, the value may indicate whatportion of the memory 210 is written to during the RDMA write withimmediate value operation. Alternatively or in addition, the clientlogic 212 and/or the allocation logic 412 may perform operations thatcreate a condition at the memory appliance 110 that the observer logic218 may check for. For example, the client logic 312 and/or theallocation logic 412 may perform a client-side memory access operationto store information about a set of memory access operations in aparticular portion of the memory on the memory appliance 110. Theinformation stored in the portion may include, for example, the offset,size, and/or type of each memory access operation performed. Theobserver logic may check the portion for updates in order to identifyone or more attributes of the memory access operations.

The observer logic 218 may observe or otherwise identify the operationsrequested by the client logic 312 and/or the allocation logic 412 thatare performed on the region 214 and/or the memory appliance 110. Theobserver logic 218 may identify the requested operations based on directcommunication between the memory appliance 110 and any of: the client130, the management server 120, and/or another memory appliance. Forexample, the observer logic 218 may listen for incoming notificationmessages at the communication interface 230. Alternatively, or inaddition, the observer logic 218 may passively monitor the operationsrequested by the client logic 312 and/or the allocation logic 412. Forexample, the observer logic 218 may listen for notification messagesreceived as a result of operations performed by the client logic 312and/or the allocation logic 412.

Alternatively, or in addition, the observer logic may check forconditions created by the client logic 312, the allocation logic 412,the communication interfaces, or another hardware component. Forexample, the observer logic 218 may read contents of one or moreportions of the memory 210 that are accessible by the client 130 and/orthe management server 120 using client-side memory access, by thecommunication interfaces, or by another hardware component. In anexample, a first portion of the memory 210 may include one or more flagsthat indicate whether one or more second portions of the memory 210 havebeen updated by the memory access operations since the one or moresecond portions of the memory 210 were last copied to the backing store260. In a second example, a first portion of the memory 210 may includeone or more flags that indicate whether one or more second portions ofthe memory 210 have been read or written by the memory access operationssince the last time the flags have been checked by the observer logic218. In a third example, a first portion of the memory 210 may includeone or more values that indicate how many times one or more secondportions of the memory 210 have been read or written by the memoryaccess operations since the last time the values have been checked bythe observer logic 218.

In response to identifying a set of memory access operations, theobserver logic 218 may take further action. In an example, furtheraction may include determining statistics related to the memory accessoperations (including but not limited to the type of operation, thenumber of operations, the size of the affected memory, and/or memorylocations of each operation). In a second example, further action mayinclude tracking or identifying regions of the memory 210 that have beenwritten to or otherwise affected by the memory access operations. Theobserver logic 218 may persist the contents of the affected regions ofthe memory 210 to the backing store 260, backing stores, and/orduplicate the contents of the affected regions of the memory 210 toanother memory appliance, a block device, an external server, and/or abackup device. Alternatively, the observer logic 218 may take any otheraction related to the memory access operations.

The memory access operation may complete at the memory appliance 110without waiting for the observer logic 218 to identify the memory accessoperation. Alternatively or in addition, the memory access operation maycomplete at the memory appliance 110 without waiting for the observerlogic 218 to take any further action in response to identifying thememory access operation. Accordingly, the client logic 312 and/or theallocation logic 412 may perform a write operation to the region 214 inthe amount of time that the request to perform the write operationtravels over the interconnect 140 and the memory appliance 110 writesdata to the memory. The overhead associated with storage protocolsand/or writing the data to the backing store 260 may be avoided.

Mechanisms for observing or identifying the operations requested by theclient logic 312 and/or the allocation logic 412 and the actions takenin response to identifying the operations may take any of numerousforms. A particular mechanism may balance tradeoffs between individualoperation latency, operations per second from an individual clientand/or management server, aggregate operations per second from multipleclients and/or management servers, demand placed upon compute resourcesof the clients, demand placed on compute resources of the managementservers, and demand placed on compute resources of the memory applianceor on the observer logic, among others.

Alternatively or in addition the observer logic 218 may not observe oridentify the memory access operations performed. Alternatively or inaddition, the observer logic 218 may take one or more actions withoutspecific knowledge of the memory access operations. For example, theobserver logic 218 may persist the entire contents of the region 214 tothe backing store 260; duplicate the entire contents of the region 214to another storage device, external server, and/or backup device; and/ortake some other action related to the region 214. Alternatively or inaddition, the observer logic 218 may compare the contents of the region214 with the contents of the backing store 260. Alternatively or inaddition, the observer logic 218 may use computed hash values todetermine which areas of the region 214 have been modified. A computedhash value may be a computed output which is expected with highprobability to have a different value for two different input buffersand which may be smaller than one or both input buffers. Examples ofcomputed hash values include checksums, cyclic redundancy check codes,and cryptographic hash codes. The observer logic 218 may perform actionswithout knowledge of the memory access operations periodically, prior tosystem shutdown, according to a schedule, or in response to a particularevent, such as a hardware interrupt.

Alternatively, a client-side memory access may be performed as describedthroughout this disclosure, and then the client logic 312 may choose towait for an additional notification from the observer logic 218 that thefurther actions are complete. For example, the client-side memory accessmay be a first client-side memory access, and the further actions mayinclude replicating data from the affected regions to one or moreadditional memory appliances using additional client-side memoryaccesses between the memory appliances. Waiting for the additionalnotification for the first client-side memory access provides assuranceto the client logic 312 that the affected regions have been synchronizedbetween the multiple memory appliances. If an application is performingactivities that may benefit from this assurance, it may be beneficial towait for the additional notification. While waiting for the additionalnotification does increase the overall latency of the first client-sidememory access by the time it takes for the observer logic 218 to benotified and replicate the affected regions and the time it takes toreceive the additional notification, the client logic 312 still does notneed to wait for the observer logic 218 of the additional memoryappliances to be notified or take any action.

The application logic, the client logic 312, and/or the allocation logic412 may perform data translation on the data being read and/or writtento the region 214. Alternatively, or in addition, the communicationinterfaces, the memory controllers, the storage controllers, and/or thebacking stores may perform data translation. Data translation mayinclude manipulating the data being read and/or written.

In a first example, the application logic, the client logic, theallocation logic, the communication interfaces, the memory controllers,the storage controllers, and/or the backing stores may compress the databeing written to the region 214 and/or decompress the data being readfrom the region 214. Compression and/or decompression may be performedusing any one or more compression schemes, such as Lempel-Ziv (LZ),DEFLATE, Lempel-Ziv-Welch (LZW), Lempel-Ziv-Renau (LZR),Lempel-Ziv-Oberhumer (LZO), Huffman encoding, LZX, LZ77, Prediction byPartial Matching (PPM), Burrows-Wheeler transform (BWT), Sequitur,Re-Pair, arithmetic code, and/or other scheme which may be used torecoverably reduce the size of data.

In a second example, the application logic, the client logic, theallocation logic, the communication interfaces, the memory controllers,the storage controllers, and/or the backing stores may encrypt the databeing written to the region 214 and/or decrypt the data being read fromthe region 214. Encryption and/or decryption may be performed using anyone or more encryption schemes and/or ciphers, such as symmetricencryption, public-key encryption, block ciphers, stream ciphers,substitution ciphers, transposition ciphers, and/or any other schemewhich may be used to encode information such that only authorizedparties may decode it. One or more encryption keys for the one or moreencryption schemes may be included in the access parameters for theregion 214.

In a third example, the application logic, the client logic, theallocation logic, the communication interfaces, the memory controllers,the storage controllers, and/or the backing stores may perform errordetection and/or error correction upon the data being written to theregion 214 and/or the data being read from the region 214. Errordetection and/or error correction may be performed using any one or moreerror detection and/or error correction schemes, such as repetitioncodes, parity bits, checksums, cyclic redundancy checks, cryptographichash functions, error correcting codes, forward error correction,convolutional codes, block codes, Hamming codes, Reed-Solomon codes,Turbo codes, low-density parity-check codes (LDPC), and/or any otherscheme which may be used to detect and/or correct data errors.

The application logic 314, the client logic 312, and/or the allocationlogic 412 may perform data monitoring on the data being read and/orwritten to the region 214. Alternatively, or in addition, thecommunication interfaces, the memory controllers, the storagecontrollers, and/or the backing stores may perform data monitoring. Datamonitoring may include observing the data being read and/or written. Inan example, the application logic, the client logic, the allocationlogic, the communication interfaces, the memory controllers, the storagecontrollers, and/or the backing stores may perform virus scanning ondata being read from and/or written to the region 214. In a secondexample, the application logic, the client logic, the allocation logic,the communication interfaces, the memory controllers, the storagecontrollers, and/or the backing stores may perform malware detection ondata being read from and/or written to the region 214. In a thirdexample, the application logic, the client logic, the allocation logic,the communication interfaces, the memory controllers, the storagecontrollers, and/or the backing stores may perform policy enforcement,such as monitoring for forbidden data patterns and/or strings, on databeing read from and/or written to the region 214. In a fourth example,the application logic, the client logic, the allocation logic, thecommunication interfaces, the memory controllers, the storagecontrollers, and/or the backing stores may perform data indexing on databeing read from and/or written to the region 214. For example an indexfor a first region may be created in a second region, the indexproviding fast lookup of data in the first region.

Presence of management servers, memory appliances, and/or clients may bedetected automatically by the allocation logic 412, the region accesslogic 212, and/or the client logic 312. When the management server 120,the memory appliance 110, and/or the client 130 is detected by theallocation logic 412, the region access logic 212, and/or the clientlogic 312, it may become known to the allocation logic 412, the regionaccess logic 212, and/or the client logic 312 that detected it. Tofacilitate being detected, the allocation logic 412, the region accesslogic 212, and/or the client logic 312 may transmit a hello message uponone or more interconnects 140 upon startup, periodically, and/or uponreceiving a presence detection request message. Upon receiving a hellomessage, the allocation logic 412, the region access logic 212, and/orthe client logic 312 may detect the management server 120, the memoryappliance 110, and/or the client 130 that sent the hello message. Tofacilitate detecting management servers, memory appliances, and/orclients, the allocation logic 412, the region access logic 212, and/orthe client logic 312 may send a presence detection request message. Apresence detection request message may include information about thecharacteristics or configurations of the management servers and/ormemory appliances including the allocation logic 412 and/or regionaccess logic 212 that may respond. Alternatively or in addition, apresence detection request message may include an indication of whetheronly management servers, only memory appliances, only clients, or somecombination of these may respond.

Alternatively, or in addition, the allocation logic 412, the regionaccess logic 212, and/or the client logic 312 may register the presenceof the corresponding management servers, memory appliances, and/orclients with one or more registration servers. A registration server maybe an InfiniBand subnet administrator, a Domain Name System (DNS)server, a Multicast DNS (mDNS) server, Service Location Protocol (SLP)directory agent, an Active Directory Server, or any other server capableof receiving and/or distributing information about management servers,memory appliances, and/or clients. Alternatively, or in addition, theallocation logic 412, the region access logic 212, and/or the clientlogic 312 may include information about the characteristics and/orconfiguration of the corresponding management servers, memoryappliances, and/or clients when registering their presence with theregistration server. The allocation logic 412, the region access logic212, and/or the client logic 312 may detect management servers, memoryappliances, and/or clients by querying the one or more registrationservers.

Alternatively, or in addition, presence of management servers and/ormemory appliances may be specified by an administrator using a userinterface. The user interface may be a graphical user interface, a webinterface, a command-line interface, an application programminginterface (API), and/or any other type of interface or combination ofinterfaces known now or later discovered.

Management servers may be associated with one or more memory appliances.Memory appliances may be associated with one or more management servers.Management servers may additionally be associated with zero or moreother management servers. For example, the management server 120 may beassociated with another management server that may function as a backupmanagement server in case the management server 120 fails. The backupmanagement server may maintain copies of data of the management server120, including, but not limited to, the external memory allocationmetadata 414 and/or the region metadata 215. The backup managementserver may further have a copy of the backing store 460 of themanagement server 120. The backup management server may obtain suchcopies of data at a predetermined schedule. Alternatively, or inaddition, the backup management server may obtain a copy of the data inresponse to an event, such as modification of the data of the managementserver 120. Alternatively, or in addition, the backup management servermay obtain a copy of the data from the management server 120 in responseto a request from an administrator, such as via the user interface. Thebackup management server 120 may obtain data of the management server120 as described elsewhere in this disclosure.

Associations between management servers and memory appliances may bespecified by an administrator using a second user interface, which maybe part of the user interface described earlier. The second userinterface may be a graphical user interface, a web interface, acommand-line interface, an API, and/or any other type of interface orcombination of interfaces known now or later discovered.

The memories of the memory appliances associated with the managementserver 120 may be part of a memory pool. Alternatively, or in addition,the memories of the memory appliances known to the allocation logic 412of the management server 120 may be part of the memory pool.Alternatively, or in addition, the memories of the memory appliancesassociated with multiple management servers and/or known to multipleallocation logics may be part of the memory pool. The pool of memory, orthe memory pool, may be a collection of allocatable memory that spansone or more memory appliances.

Alternatively, or in addition, associations between management serversand memory appliances may be determined automatically. Automaticassociations between management servers and memory appliances may bedetermined based upon characteristics or configurations of themanagement servers, the memory appliances, or both. Characteristics orconfigurations of the management server 120, the memory appliance 110,and/or the client 130 may include hardware revisions, firmwarerevisions, software revisions, protocol revisions, physical location,logical location, network location, network topology, network bandwidth,network capacity, network utilization, logical grouping, labels, names,server/appliance health, server/appliance utilization, server/applianceoverall performance rating, processor type, number of processors,processor speed, memory bandwidth, memory capacity, memory utilization,memory health, backing store presence, backing store bandwidth, backingstore input/output operations per second (IOPS), backing store latency,backing store capacity, backing store utilization, backing store health,battery presence, battery type, battery chemistry, battery capacity,battery utilization, battery % charged, battery time remaining, batteryhealth, or any other characteristic or combination of characteristics ofthe management server 120, the memory appliance 110, and/or the client130. In an example, the allocation logic 412 may automatically associatethe management server 120 with memory appliances in the same physicalrack. In another example, the allocation logic 412 may automaticallyassociate the management server 120 with memory appliances sharing thesame protocol version. In another example, the allocation logic 412 mayautomatically associate the management server 120 with memory applianceswith appliance health, memory health, backing store health, and/orbattery health above or below a threshold or set of thresholds. Thethresholds may be configurable by the administrator via the userinterface, or may be predetermined when the management server starts up.

The allocation logic 412 may transmit region access logic requests tothe region access logic 212 included in one or more memory appliances.The memory appliances including the region access logic 212 to which therequests are sent may be associated with the management serversincluding the allocation logic 412 and/or known by the allocation logic412. For example, region access logic requests received by the regionaccess logic 212 may include requests to create the region 214, requeststo resize the existing region 214, requests to restore contents of theregion 214 from the backing store 260, requests to get the status of thememory 210 included in the memory appliance 110, requests to get healthstatus from the memory appliance 110, requests to persist the region 214to the backing store 260 and remove the region 214 from the memory 210,requests to destroy the region 214, requests to get a list of availableregions, requests to get information for the region 214, requests tomodify settings for the region 214, requests to migrate the region 214,and/or any other request related to the memory appliance 110 and/or theregions included in the memory 210 of the memory appliance 110.

The region access logic requests may be communicated over anycommunications protocol and/or interface capable of carrying messages.For example, the region access logic requests may be carried over UDPdatagrams, a TCP connection, an SSL connection, InfiniBand reliableconnections, RoCE, iWARP, HTTP, or any other communications protocolknown now or later discovered. Alternatively, or in addition, the regionaccess logic requests may be carried over remote procedure calls, suchas using XML-RPC, SOAP, CORBA, Java Remote Method Invocation (Java RMI),and/or any other remote procedure call protocol. Alternatively, or inaddition, the region access logic requests may be carried over acommunication protocol based on client-side memory access, such as bywriting messages into a buffer on the memory appliance 110 viaclient-side-memory access. Alternatively, or in addition, the regionaccess logic requests may be carried via invoking methods in an API. Forexample, if the allocation logic 412 and region access logic 212 areco-located or combined, the region access logic requests may be methodsin an API. The allocation logic 412 and region access logic 212 may beco-located in examples where the memory appliance 110 also functions asthe management server 120, or, alternatively, the management server 120also functions as the memory appliance 110.

Upon receiving a request to create the region 214, the region accesslogic 212 may allocate a portion of the memory 210 included in thememory appliance 110 for the region 214. Allocating a portion of thememory 210 may include initializing the contents of the allocatedmemory. Alternatively, or in addition, the memory being allocated may bepre-initialized, such as by an operating system. Alternatively, or inaddition, the memory being allocated may be partially pre-allocated,such as a free list including one or more portions of pre-allocatedand/or pre-initialized memory. Alternatively, or in addition, the regionaccess logic 212 may configure the communication interface 230 for theregion 214 without allocating the entire portion of the memory for theregion 214 and/or without initializing the contents of the memory. Theregion access logic 212 may configure the communication interface 230 totreat un-allocated and/or un-initialized portions as not present.Attempting to access data that is not present using client-side memoryaccess may fail. Alternatively, or in addition, attempting to accessdata that is not present using client-side memory access may cause theprocessor 240 to be notified. Upon being notified, the processor 240 maytake some action related to the attempt to access data that is notpresent, such as allocating a portion of the memory 210 to satisfy theattempt to access data that is not present and/or initializing theportion of the memory. The region access logic 212 may also associate anidentifier with the region 214. The identifier may be chosen by theregion access logic 212 or it may be included in the request to createthe region 214. Additionally, the region access logic 212 may associatemetadata with the region 214. The region access logic 212 may respond tothe request to create the region 214 with a response message. Theresponse message may include the identifier associated with the region214 and/or a status, indicating whether the operation was successful.

Upon receiving a request to resize the existing region 214, if theregion 214 is being expanded, the region access logic 212 may allocate aportion of the memory 210 of the memory appliance 110. Allocating aportion of the memory 210 may include initializing the contents of theallocated memory. Alternatively, or in addition, the memory beingallocated may be pre-initialized, such as by an operating system.Alternatively, or in addition, the memory being allocated may bepartially pre-allocated, such as a free list including one or moreportions of pre-allocated and/or pre-initialized memory. The size of theportion of the memory may be related to the size of the expanded regionminus the size of the existing region 214. For example, the size of theportion of the memory may be the size of the expanded region minus thesize of the existing region 214 rounded up to the nearest unit ofallocation, such as a page, a huge page, a slab, and/or any other unitof allocation. The units of allocation may have respective predeterminedsizes. The predetermined sizes may vary, such as based on an operatingsystem being used by the client 130, the memory appliance 110, and/orthe management server 120. Alternatively, or in addition, the size ofthe portion of the memory may be specified by the request to resize theexisting region 214. Alternatively, or in addition, the request toresize the existing region 214 may specify an offset within the region214 where the allocated portion may appear. For example, the request toresize the existing region 214 may be re-allocating a portion of theregion 214 that was previously de-allocated by a different request toresize the same region 214. The region access logic 212 may assign theallocated portion to the region 214. The region access logic 212 mayupdate the region metadata 215 to include references to the allocatedportion of the memory 210.

Upon receiving the request to resize the existing region 214, if theregion 214 is being contracted, the region access logic 212 may updatethe region metadata 215 to remove references to a portion of the memoryallocated to the region 214 and/or may de-allocate the portion of thememory. De-allocating may include listing the de-allocated portions onthe free list. The portion of the memory may be the portion at thelogical end of the region 214, at the logical beginning of the region214, and/or at any other logical location within the region 214. Theportion of the region to be removed may be specified by the request toresize the existing region 214. For example, the request to resize theexisting region 214 may specify that the data at the end of the region214 may be discarded. Alternatively, or in addition, the request toresize the existing region 214 may specify that the data at thebeginning of the region 214 may be discarded. Discarding data at alocation other than the end of the region 214 may cause the offsets ofdata after the discarded data to change. For example, removing 100 MiB(mebibyte) from the region starting at an offset of 200 MiB may causedata that previously occurred at an offset of 300 MiB to instead occurat an offset of 100 MiB. Alternatively, discarding data at a locationother than the end of the region 214 may cause the offsets of data afterthe discarded data to stay the same. The region access logic 212 mayconfigure the communication interface 230 to treat the discarded data asnot-present. Attempting to access data that is not present usingclient-side memory access may fail. Alternatively, attempting to accessdata that is not present using client-side memory access may cause theprocessor 240 to be notified. Upon being notified, the processor 240 maytake some action related to the attempt to access data that is notpresent, such as allocating a portion of the memory and/or initializingthe portion to satisfy the attempt to access the data that is notpresent.

Upon receiving a request to restore the contents of the region 214 fromthe backing store 260, the region access logic 212 may allocate aportion of the memory 210 included in the memory appliance 110 for theregion 214. The region access logic 212 may copy the contents ofpersisted data related to the region 214 into the allocated memory.Alternatively, or in addition, the region access logic 212 may associateportions of the backing store 260 with portions of the region 214without immediately allocating the portion of the memory and/or withoutimmediately copying the contents by configuring the communicationinterface 230 to treat the portions of the region 214 as not present.Attempting to access data that is not present using client-side memoryaccess may fail. Alternatively, attempting to access data that is notpresent using client-side memory access may cause the processor 240 tobe notified. Upon being notified, the processor 240 may take some actionrelated to the attempt to access data that is not present, such asallocating a portion of the memory to satisfy the attempt to access datathat is not present, initializing the portion of the memory, and/orcopying the contents of persisted data related to the portion into theportion. The region access logic 212 may respond to the request torestore the contents of the region 214 from the backing store 260 with aresponse message. The response message may include the identifierassociated with the region 214 and/or a status, indicating whether theoperation was successful.

Upon receiving a request to get the status of the memory 210 included inthe memory appliance 110, the region access logic 212 may respond to therequest with a response message. The response message may include one ormore attributes of the memory 210 included in the memory appliance 110.The attributes may include the total memory available to hold regions,the amount of memory currently in use by existing regions, the amount ofmemory available to hold additional regions, and/or any other attributesof the memory 210 included in the memory appliance 110.

Upon receiving a request to get health status from the memory appliance110, the region access logic 212 may respond to the request with aresponse message. The response message may include one or moreattributes describing the health of the memory appliance 110, ofcomponents included in the memory appliance 110, and/or of componentsconnected to the memory appliance 110. Examples of health that may bedescribed by the attributes include temperatures, voltages, coolingsystem health, backing store status, memory health, CPU health, batterycapacity, projected battery run time, or any other hardware, firmware,or software status and/or health relevant to the health of the memoryappliance 110. Temperatures may include CPU temperatures, integratedcircuit temperatures, circuit board temperatures, chassis intaketemperatures, chassis output temperatures, power supply temperatures,uninterruptible power supply (UPS) temperatures, battery temperatures,backing store temperatures, and/or any other temperatures relevant tothe health of the memory appliance 110. Voltages may include CPUvoltages, integrated circuit voltages, circuit board voltages, powersupply input voltages, power supply output voltages, UPS input voltages,UPS output voltages, battery voltages, and/or any other voltagesrelevant to the health of the memory appliance 110. Cooling systemhealth may include fan speeds, liquid coolant temperatures, liquidcoolant flow rates, facility cooling health, and/or any other statusrelated to the ability to maintain stable temperatures. Backing storestatus may include status of individual storage devices included in thebacking store, status of hardware and/or software storage controllers,status of logical volumes included in the storage devices, status oflogical associations between storage devices, status of logicalassociations between logical volumes, and/or any other status related tothe ability to reliably store data in the backing store 260. Logicalassociations may include software or hardware mechanisms used toaggregate storage devices or logical volumes and/or to provideredundancy and/or resiliency. For example, a logical association may bea redundant array of independent disks (RAID). Memory health may includenumber and/or source of memory errors, memory redundancy status, and/orany other status related to the ability to reliably store data in thememory. Memory errors may include recoverable error correcting code(ECC) errors, unrecoverable ECC errors, rank spared indications, mirrorbroken indications, and/or any other errors and/or indications reportedby the memory and/or memory controller. CPU health may include CPUerrors, CPU voltage/frequency scaling mode, and/or any other statusrelated to the CPU's ability to reliably execute instructions. CPUerrors may include hardware watchdog expirations, machine checks, cacheECC errors, processor faults, and/or any other error or indicationreported by the CPU and/or CPU monitoring hardware.

Upon receiving a request to persist the region 214 to the backing store260 and remove it from memory 210, the region access logic 212 may copythe contents of the region 214 to a portion of the backing store 260.The portion of the backing store 260 may be determined at the time therequest to persist the region 214 to the backing store 260 and remove itfrom the memory 210 is received. Alternatively, the portion may havebeen determined in advance, such as when the region 214 was created,and/or when the region 214 was configured. After the contents of theregion 214 are copied to the portion of the backing store 260, theregion access logic 212 may de-allocate the portion of the memoryincluded in the memory appliance 110 for the region 214. De-allocatingmay include listing the de-allocated portions on a free list, whichindicates portions of the memory 210 that have not been allocated to anyparticular region. Alternatively, or in addition, as the contents ofportions of the region 214 are copied to the backing store 260, theregion access logic 212 may selectively de-allocate the portions of theregion 214 that have already been copied to the backing store 260.Alternatively or in addition, if portions of the region 214 have alreadybeen copied to the backing store 260 prior to receiving the request topersist the region 214 to the backing store 260 and remove it frommemory 210, the region access logic 212 may not copy the portions of theregion 214 that have already been copied to the backing store 260. Theregion access logic 212 may respond to the request to persist the regionto the backing store 260 and remove it from memory 210 with a responsemessage. The response message may include the identifier associated withthe region 210 and/or a status, indicating whether the operation wassuccessful.

Upon receiving a request to destroy the region 214, the region accesslogic 212 may de-allocate the portion of the memory included in thememory appliance 110 for the region 214. De-allocating may includelisting the de-allocated portions on the free list. Alternatively, or inaddition, the region access logic 212 may delete any persisted datarelated to the region 214 included in the backing store 260. The regionaccess logic 212 may respond to the request to destroy the region 214with a response message. The response message may include the identifierassociated with the region 214 and/or a status, indicating whether theoperation was successful.

Upon receiving a request to get a list of available regions, the regionaccess logic 212 may respond to the request with a response message. Theresponse message may include a number of available regions and/orattributes related to the available regions. Available regions mayinclude regions that are included in the memory 210, regions that areincluded in the backing store 260, and/or regions that are partiallyincluded in the memory 210 and/or backing store 260. The attributesrelated to an available region, such as the region 214, may include theidentifier associated with the region, the size of the region, thestatus of the region, information about external memory allocations thatreference the region, and/or any other information related to theregion. The status of the region 214 may include one or more indicationsof whether the region is included in the memory 210, whether the region214 is included in the backing store 260, whether the contents of theregion 214 are being persisted to the backing store 260, whether thecontents of the region 214 are being restored from the backing store260, and/or whether the contents of the region 214 are being transferredto or from another memory appliance or storage device. Information aboutan external memory allocation may include an identifier for the externalmemory allocation, information about the external memory allocation,and/or information about the region's role in the external memoryallocation. For example, an external memory allocation may includemetadata describing a logical relationship between the regionsreferenced by the external memory allocation. In one example, thelogical relationship could be a concatenation of regions located indifferent memory appliances, the metadata describing the logicalrelationship may include an indication that concatenation is in useand/or a logical address within the external memory allocation at whichthe region's data logically exists. Alternatively, or in addition, thelogical relationship could be a striping relationship, such as RAID-0; amirroring relationship, such as RAID-1; a parity relationship, such asRAID-2, RAID-3, RAID-4, RAID-5, or RAID-6; a partial data redundancyrelationship, a combination of relationships, such as striping withmirroring; or any other relationship between regions known now or laterdiscovered.

Upon receipt of a request to get information for the region 214, theregion access logic 212 may respond to the request with a responsemessage. The response message may include information related to theregion 214. The information related to the region 214 may include all ofor a portion of the region metadata 215. Alternatively, or in addition,the information related to the region 214 may be derived from the regionmetadata 215. Alternatively, or in addition, the information related tothe region 214 may be different depending upon parameters included inthe request to get information for the region 214. For example, theparameters may include an indication of which portion of the metadata215 may be included in the information related to the region 214.

Upon receiving a request to modify settings for the region 214, theregion access logic 212 may update the region metadata 215 to reflectthe modified settings. For example, the request to modify settings forthe region 214 may set a human readable label to be associated with theregion 214, modify access parameters, and/or modify other portions ofthe region metadata 215. The region access logic 212 may restrict whichparts of the region metadata 215 may be modified. For example, theregion access logic 212 may use the access parameters to control whichparts of the region metadata 215 may be modified. If the region accesslogic 212 determines that the requested changes are not allowed, therequest to modify settings of the region 214 may fail. In anotherexample, the request to modify settings of the region 214 may include arequest to enable replication and/or may include identifiers for regionsand/or memory appliances to which the data of the region 214 of thememory appliance 110 may be replicated. When replication is enabled, theobserver logic 218 may replicate affected portions of the region 214 tothe regions and/or memory appliances indicated in the request to modifysettings for the region 214 using the methods described throughout. Theregion access logic 212 may respond to the request to modify settingsfor the region 214 with a response message. The response message mayinclude the identifier associated with the region 214, informationrelated to the modified region metadata 215, and/or a status, indicatingwhether the operation was successful.

FIGS. 5A and 5B illustrate an example scenario of a request to migrate aregion. A request to migrate a region may indicate a request 502 a tomigrate data from a first region 214 a included in a memory of a firstmemory appliance, 110 a to a second region 214 b included in a memory ofa second memory appliance 110 b, as illustrated in FIG. 5A. The requestto migrate the first region 214 a to the second region 214 b may be arequest 502 a received by the region access logic 212 a of the firstmemory appliance 110 a and/or a request 502 b received by the regionaccess logic 212 b of the second memory appliance 110 b.

FIG. 5B illustrates an exemplary flowchart of steps taken upon receiptof a request 502 a to migrate the first region 214 a by the regionaccess logic 212 a of the first memory appliance 110 a (502). The regionaccess logic 212 a may determine if the second region has to be newlycreated within the second memory appliance (504). The request 502 a tomigrate the first region 214 a may include an identifier for the secondmemory appliance 110 b. Alternatively or in addition, the request 502 ato migrate the first region 214 a may include an identifier for thesecond region 214 b. Alternatively, or in addition, the request 502 a tomigrate the first region 214 a may indicate creating the second region214 b at the second memory appliance 110 b, in case the second region214 b does not exist (530). If creation of the second region 214 bfails, the migration request 502 a may fail (530, 550). Alternatively,if the second region 214 b is successfully created, the contents of thefirst region 214 a may be transferred to the second region 214 b as partof a successful migration (540, 545).

If the request 502 a to migrate the first region 214 a includes theidentifier for the second region 214 b, the region access logic 212 amay send a request to get a list of available regions and/or a requestto get information of the second region 214 b to the region access logic212 b of the second memory appliance 110 b (510). The receivedinformation of the second region 214 b may be analyzed to determine ifthe second region 214 b is compatible to complete the migration request502 a (512). For example, if the response to the request to get the listof available regions indicates failure and/or does not include theidentifier for the second region 214 b, then the request 502 a tomigrate the first region 214 a may fail (550). Alternatively, or inaddition, if the response to the request to get information for thesecond region 214 b indicates failure and/or includes informationindicating that the second region 214 b cannot be used to hold all ofthe data of the first region 214 a, then the request 502 a to migratethe first region 214 a may fail (550).

Information indicating that the second region 214 b is incompatible forcompletion of the migration request 502 a, such as cannot be used tohold all of the data of the first region 214 a, may include a size ofthe second region 214 b that is smaller than the size of the firstregion 214 a, access permissions for the second region 214 b thatindicate that the first memory appliance 110 a may not write to thesecond region 214 b, or any other limiting information. In such cases ofincompatibility, the first memory appliance 110 a may requestreconfiguring the second region 214 b so as to conform the second region214 b for the migration (516). For example, if the size of the secondregion 214 b is smaller than the size of the first region 214 a, theregion access logic 212 a of the first memory appliance 110 a may send arequest to resize the second region 214 b to the region access logic 212b of the second memory appliance 110 b. If the response to thereconfiguration request, such as the request to resize the second region214 b, indicates failure (520), the request 502 a to migrate the firstregion 214 a may fail (550). In case, the reconfiguration is successful,the first memory appliance 110 a may confirm that the second region 214b is now compatible for the migration (522). Once compatibility isconfirmed, the region access logic 212 a may attempt to perform a firstclient-side memory access to write data from the first region 214 a tothe second region 214 b (540) and on successful completion, mark themigration as successful (545).

Copying data from the first region 214 a to the second region 214 b mayfurther involve transferring any changes that may be made to the firstregion 214 a which are not captured by the first client-side memoryaccess (540). For example, the client 130 may continue to access theregion 214 a during the client-side memory access, including writing tothe region 214 b. Concurrently with the client-side memory access, theobserver logic 218 a of the first memory appliance 110 a may observewhich portions of the first region 214 a are modified during theclient-side memory access. Upon completing the first client-side memoryaccess, the region access logic 212 a may attempt to perform client-sidememory access to write the modified portions from the first region 214 ato the second region 214 b (540). The region access logic 212 a andobserver logic 218 a may repeat this procedure until no portions areleft to be migrated. Alternatively, or in addition, the region accesslogic 212 a of the first memory appliance 110 a may modify the accesspermissions of the first region 214 a to prohibit writing additionalchanges to the first region 214 a. For example, the access permissionsmay be changed after the number or total data size of the portions leftto be migrated is above or below a configured threshold. The migrationmay complete when there are no portions left to be migrated. If the oneor more attempts to perform client-side memory access fails, the requestto migrate a region may fail.

Upon receipt of the request 502 b to migrate the first region 214 a bythe region access logic 212 b of the second memory appliance 110 b,similar steps may be performed by the second memory appliance 110 b. Theregion access logic 212 b may determine if a new region needs to becreated (504). The request to migrate the first region 214 a may includean identifier for the first memory appliance 110 a and/or the firstregion 214 a. Alternatively or in addition, the request to migrate theregion may include an identifier for the second region 214 b.Alternatively, or in addition, the request 502 b to migrate the firstregion 214 a may indicate that a new region may be created at the secondmemory appliance 110 b. The region access logic 212 b may send a requestto get a list of available regions and/or a request to get informationfor the first region to the region access logic 212 a of the firstmemory appliance 110 a. If the response to the request to get a list ofavailable regions indicates failure and/or does not include theidentifier for the first region 214 a, then the request 502 b to migratethe first region may fail (550). Alternatively, or in addition, if theresponse to the request to get information for the first region 214 aindicates failure and/or includes information indicating that the secondregion 214 b cannot be used to hold all of the data of the first region214 a, then the request 502 b to migrate the first region 214 a may fail(550). Information indicating that the second region 214 b isincompatible for completion of the migration request 502 b, such as,cannot be used to hold all of the data of the first region 214 a, mayinclude a size of the first region 214 a that is larger than the size ofthe second region 214 b, access permissions for the first region 214 athat indicate that the second memory appliance 110 b may not read fromthe first region 214 a, or any other incompatibility criteria (512). Insuch cases of incompatibility, the second memory appliance 110 b mayreconfigure the second region 214 b so as to conform the second region214 b for the migration 516). For example, if the size of the secondregion 214 b is smaller than the size of the first region 214 a, theregion access logic 212 b of the second memory appliance 110 b mayattempt to resize the second region 214 b using the methods of therequest to resize an existing region. If the attempt to resize thesecond region 214 b fails, the request 502 b to migrate a region mayfail. In case, the reconfiguration is successful, the second memoryappliance 110 b may confirm that the second region 214 b is nowcompatible for the migration (520, 522). Upon ensuring compatibility ofthe regions, the region access logic 212 b may attempt to performclient-side memory access to read data from the first region 214 a intothe second region 214 b and on successful completion, mark the migrationas successful (522, 540, 545). If the attempt to perform client-sidememory access fails, the request 502 b to migrate a region may fail(550).

Prior to starting the client-side memory access, the region access logic212 b of the second memory appliance 110 b may send a request to modifysettings for the first region 214 a to the region access logic 212 a ofthe first memory appliance 110 a. The request to modify settings for thefirst region 214 a indicating that replication may be enabled from thefirst region 214 a to the second region 214 b. If the response to therequest to modify settings for the first region 214 a indicates failure,the request 502 b to migrate the first region 214 a may fail.

Upon completing the client-side memory access, the region access logic212 b of the second memory appliance 110 b may send one or more requeststo get information for the first region 214 a to the region access logic212 a of the first memory appliance 110 a, the requests to getinformation for the first region 214 a requesting information about howmuch data has been written to the first region 214 a but not yetreplicated to the second region 214 b. If the response to one or more ofthe requests to get information for the first region indicates failure,the request 502 b to migrate the first region 214 a may fail.Alternatively, one or more of the requests to get information for thefirst region 214 a may be retried. The region access logic 212 b of thesecond memory appliance 110 b may send the requests to get informationfor the first region 214 a until the response to one or more of therequests to get information for the first region 214 a indicates that nodata has been written to the first region 214 a that is not replicatedto the second region 214 b. Alternatively, or in addition, the regionaccess logic 212 b of the second memory appliance 110 b may send asecond request to modify settings for the first region 214 a to theregion access logic 212 a of the first memory appliance 110 a, thesecond request to modify settings for the first region 214 a requestingthat the access permissions of the first region 214 a be changed toprohibit additional changes to the first region 214 a. For example, theaccess permissions may be changed after the number or total data size ofthe portions left to be migrated is above or below a configuredthreshold. If the response to the second request to modify settings forthe first region 214 a indicates failure, the request 502 b to migratethe first region 214 a may fail. The migration 502 b may complete whenthere are no portions left to be migrated.

The region access logic 212 a and/or 212 b, that receives a request tomigrate a region, may respond to the request 502 a and/or 502 b with aresponse message. The response message may include the identifierassociated with the first region 214 a, the identifier associated withthe second region 214 b, and/or a status, indicating whether theoperation was successful.

The client logic 312 of the client 130 may transmit allocation logicrequests to the allocation logic 412 included in the management server120. Allocation logic requests may include requests to find availablememory appliances, requests to query available space on a memoryappliance, requests to create an external memory allocation, requests toresize an existing external memory allocation, requests to renew anexternal memory allocation, requests to destroy an external memoryallocation, requests to persist and free an existing external memoryallocation, requests to list existing external memory allocations,requests to get information regarding an external memory allocation,requests to restructure an external memory allocation, or any otherrequest related to the management servers, the memory appliances, theexternal memory allocations, and/or the regions on the memoryappliances. The allocation logic requests may be carried over anycommunications protocol and/or interface capable of carrying messages.For example, the allocation logic requests may be carried over UDPdatagrams, a TCP connection, an SSL connection, InfiniBand reliableconnections, RoCE, iWARP, HTTP, or any other communications protocolknown now or later discovered. Alternatively, or in addition, allocationlogic requests may be carried over remote procedure calls, such as usingXML-RPC, SOAP, CORBA, Java Remote Method Invocation (Java RMI), and/orany other remote procedure call protocol. Alternatively, or in addition,the allocation logic requests may be carried over a communicationprotocol based on client-side memory access, such as by writing messagesinto a buffer on the management server 120 via client-side-memoryaccess. Alternatively, or in addition, the allocation logic requests maybe carried via invoking methods in an API. For example, if the clientlogic 312 and the allocation logic 412 are co-located or combined, theallocation logic requests may be methods in an API.

FIG. 6 illustrates an example external memory allocation system 600. Thesystem 600 illustrates the client 130, the management server 120, and amemory pool 610. The memory pool 610 includes multiple memory appliances110 a-110 c. While FIG. 6 illustrates only three memory appliances asbeing part of the memory pool 610, in other examples, the memory pool610 may include fewer or more number of memory appliances. The client130 includes the client logic 312 and local memory 602. The managementserver 120 includes the allocation logic 412 and the external memoryallocation metadata 414. Each of the memory appliances 110 a-110 cincludes respective region allocation logic 212 a-212 c and memories 210a-210 c. The client 130, management server 120, and the memoryappliances 110 a-110 c may include other components that are notillustrated in FIG. 6. The client 130 may request an external memoryallocation, such as one of X1-X3, from the memory pool 610 via themanagement server 120 to complement the local memory 602. For example,the local memory 602 may not be sufficient to handle the tasks operatingon the client 130, and therefore the client 130 may seek the externalmemory allocations X1-X3. Alternatively, or in addition, the client 130may seek to use the external memory allocations X1-X3 as the primarymemory with the local memory 602 as a cache.

The external memory allocations may reference one or more regions. Theone or more regions referenced by an external memory allocation may beincluded in a single memory appliance, or the regions may be distributedbetween multiple memory appliances.

The management server 120 may include external memory allocationmetadata 414. External memory allocation metadata 414 may includeinformation describing the external memory allocations, such asindication of the regions referenced by the external memory allocation.For example, the external memory allocation X1 may reference regionsR1-R3 as illustrated in FIG. 6, where R1 is within memory appliance 110a, R2 is within memory appliance 110 b, and R3 is within memoryappliance 110 c. The external memory allocation X2 may reference asingle region R5 from the memory appliance 110 b, while the externalmemory allocation X3 may reference regions R4 and R6 on the memoryappliances 110 a and 110 c respectively. It is understood that thedescribed distributions of the regions are exemplary and that variousother distributions of the regions referenced by an external memoryallocation are possible. Further, while the example illustrates threeexternal memory allocations X1-X3, other examples may involve fewer ormore number of external memory allocations being present in the externalmemory allocation metadata 414. The memory appliances 110 a-110 cincluding the regions R1-R6 may be known to the allocation logic 412 ofa management server 120 or associated with the management server 120that is associated with the external memory allocation.

Further metadata may also be recorded in the external memory allocationmetadata 414. For example, information describing the external memoryallocation X1 may include the size of the external memory allocation X1,a lease expiration date and/or time for the external memory allocationX1, information about the regions R1-R3 referenced by the externalmemory allocation X1, and/or any other information relevant to theexternal memory allocation X1. Alternatively, or in addition, theexternal memory allocation X1 may include metadata describing one ormore logical relationships between the regions R1-R3 referenced by theexternal memory allocation X1. The various entries in the externalmemory allocation metadata 414 may contain the same fields ofinformation, or different fields of information. The fields ofinformation described are exemplary and other types of information maybe recorded in other examples. The external memory allocation metadata414 may be included in the memory 410 included in the management server120. Alternatively, or in addition, external memory allocation metadata414 may be included in the backing store 460, if included in themanagement server 120.

The external memory allocation metadata 414 may be recoverable from theregion metadata 215 included in one or more memory appliances 110 a-110c. In an example, the external memory allocation metadata 414 may beincluded in the region metadata 215 of the memory appliances 110 a-110 cincluding one or more of the regions R1-R3 referenced by the externalmemory allocation. Accordingly, if the management server 120 fails, abackup management server may take its place by retrieving the externalallocation metadata 414 from the region metadata 215 included in one ofthe memory appliances 110 a-110 c. In a second example, the externalmemory allocation metadata 414 may be distributed amongst the regionmetadata 215 a-215 c of the memory appliances 110 a-110 c including theregions R1-R3 referenced by the external memory allocation. Accordingly,if the management server 120 fails, a backup management server may takeits place by retrieving the external allocation metadata 414 from thedistributed portions included in the region metadata 215 a-215 cincluded in the memory appliances 110 a-110 c. In a third example, theexternal memory allocation metadata 414 may be derived from the regionmetadata 215 a-215 c of the memory appliances 110 a-110 c including oneor more of the regions R1-R3 referenced by the external memoryallocation. For example, the region metadata 215 a may includeinformation about other regions R2-R3 referenced by the same externalmemory allocation as the region R1. Alternatively, or in addition, theregion metadata 215 a may include information about the logicalrelationships between the regions R1-R3. Accordingly, if the managementserver 120 fails, a backup management server may take its place byretrieving the region metadata 215 a-215 c included in one or more ofthe memory appliances 110 a-110 c and deriving the external memoryallocation metadata 414 from the retrieved region metadata 215 a-215 c.The allocation logic 412 included in the management server may retrieveregion metadata 215 a-215 c from the respective memory appliance 110a-110 c by sending a request to get information for a region to therespective region access logic 212 a-212 c included in the memoryappliances 110 a-110 c.

The region metadata 215 a-215 c may include one or more flags,identifiers, semaphores and/or other data structures that may be used toidentify the most up-to-date information that may be used to recover theexternal memory allocation metadata 414. For example, the regionmetadata 215 a-215 c may include an identifier of a primary regionand/or a secondary region, of which the corresponding metadata containsa primary copy of the information and/or a secondary copy of theinformation. Alternatively, or in addition, all copies of theinformation and/or the corresponding regions may be ranked in order fromprimary, through last. Updates to the copies of the information may beperformed in order from primary through last. Recovery of externalmemory allocation data 414 may be performed by attempting to recoverfrom the copies of the information in order from primary through last.For example, if an attempt to recover external memory allocationmetadata 414 from a primary copy of the information fails, a secondattempt may be made using the secondary copy, and so on.

An external memory allocation may be associated with one or moremanagement servers. An external memory allocation may be associated withthe management server that was used to create the external memoryallocation. Alternatively, or in addition, an external memory allocationmay be associated with other management servers, such as a backupmanagement server, a centralized management server, a localizedmanagement server, a task-specific management server, and/or any othermanagement server. An external memory allocation may become associatedwith a management server by replicating information about the externalmemory allocation from one or more management servers associated withthe external memory allocation or from one or more memory appliancesincluding the regions referenced by the external memory allocation.

The external memory allocation metadata 414 may be recoverable frominformation about the external memory allocation replicated onto othermanagement servers. For example, a copy of the external memoryallocation metadata 414 may exist on one or more management servers. Theexternal memory allocation metadata 414 may include one or more flags,identifiers, semaphores and/or other data structures that may be used toidentify the most up-to-date copy of the external memory allocationmetadata 414. For example, the external memory allocation metadata 414may include an identifier of a primary management server and/or asecondary management server which contains a corresponding primary copyand/or a secondary copy. Alternatively, or in addition, all copiesand/or the corresponding management servers may be ranked in order fromprimary, through last. Updates to the copies of the information may beperformed in order from primary through last. Recovery of externalmemory allocation metadata may be performed by attempting to recoverfrom the copies of the information in order from primary through last.For example, if the primary management server fails, an attempt may bemade to use a new management server in place of the primary managementserver and to recover the external memory allocation metadata 414 fromthe secondary management server. If the attempt to recover the externalmemory allocation metadata 414 from the secondary management serverfails, a second attempt may be made using the tertiary managementserver, and so on. Alternatively, or in addition, recovery of externalmemory allocation metadata 414 may be performed by attempting to assigna new primary management server for the external memory allocation inorder from primary through last. For example, if the primary managementserver fails, an attempt may be made to assign a new primary managementserver to be the secondary management server. Furthermore, if theattempt to assign the new primary management server for the externalmemory allocation to be the secondary management server fails, a secondattempt may be made using the tertiary management server, and so on. Ifall management servers associated with an external memory allocationhave failed, recovery may proceed using the region metadata, asdescribed.

Upon receiving a request to find available memory appliances, theallocation logic 412 may reply with a list of memory appliancesassociated with the management server 120 including the allocation logic412 receiving the request. Alternatively or in addition, the allocationlogic 412 may reply with a list of memory appliances known to theallocation logic 412. Alternatively or in addition, the allocation logic412 may reply with a list of memory appliances meeting a set ofcharacteristics and/or configurations specified by the request.

Upon receiving a request to query available space on the memoryappliances, the allocation logic 412 may determine the available spaceon the memory appliances, such as 110 a-110 c, associated with themanagement server 120 including the allocation logic 412 and/or known tothe allocation logic 412. The allocation logic 412 may determine theavailable space on a memory appliance, such as 110 a, by sending arequest to get the status of the memory 210 a included in the memoryappliance 110 a to the region access logic 212 a of the memory appliance110 a. Upon receiving the response message in response to the request toget the status of the memory 210 a included in the memory appliance 110a, the allocation logic 412 may inspect the response message todetermine the available space on the memory appliance 110 a.Alternatively, or in addition, the allocation logic 412 may determinethe available space on the memory appliance 110 a by reading regionmetadata 215 a, if included in the memory 410 of the management server120. The region metadata 215 a may be updated upon startup of theallocation logic 412 and/or management server 120, upon detection ofmemory appliances 110 a-110 c, upon association with memory appliances110 a-110 c, periodically, upon receiving a management request, whenrequested by the user interface, upon creating a region with a memoryappliance, upon occurrence of any other event, and/or at any other time.The region metadata 215 a may be updated by sending requests to get thestatus of the memory 210 a included in the memory appliance 110 a.Alternatively, or in addition, the region metadata 215 a may be updatedby receiving an asynchronous notification of the status of the memory210 a, such as the response message to the request to get the status ofthe memory 210 a included in the memory appliance 110 a. The responsemessages to the request to get the status of the memory 210 a includedin the memory appliance 110 a may be sent by the region access logic 212a in response to any event, such as a change in the region metadata 215a included in the memory 210 a of the memory appliance 110 a. Uponreceiving the response messages to the requests to get the status of thememory included in the memory appliances 110 a-110 c, the allocationlogic 412 may inspect the response messages to determine the availablespace on the memory appliances 110 a-110 c and/or update the regionmetadata 215 a-215 c. The allocation logic 412 may respond to therequest to query available space on memory appliances 110 a-110 c with aresponse message. The response message may include a summary of thestatus of the memory on the memory appliances 110 a-110 c to which theallocation logic 412 sent the requests to get the status of the memoryincluded in the memory appliance 110 a to the region access logic 212 aof the memory appliance 110 a and/or of the memory 210 a-210 c on thememory appliances 110 a-110 c which are described in the region metadata215 a-215 c. For example, the response message may include an aggregateof the total memory available to hold regions, the amount of memorycurrently in use by existing regions, and/or the amount of memoryavailable to hold additional regions. Alternatively, or in addition, theresponse message may include the status of the memory on each of thememory appliances 110 a-110 c to which the allocation logic 412 sent therequests to get the status of the memory included in the memoryappliance to the region access logic of the memory appliance and/or ofthe memory on the memory appliances 110 a-110 c which are described inthe region metadata. Alternatively, or in addition, the response messagemay include a status, indicating whether the operation was successful.

Upon receiving a request to create an external memory allocation, theallocation logic 412 may determine how to structure the external memoryallocation. The request may be received from the client 130.Alternatively, or in addition, the request may be sent by a user via theuser interface to provision external memory for the client 130. In anexample, the allocation logic 412 may determine to structure theexternal memory allocation as a single region on a single memoryappliance (such as external memory allocation X2 of FIG. 6). In a secondexample, the allocation logic 412 may determine to structure theexternal memory allocation as multiple regions on multiple memoryappliances (such as external memory allocations X1 and X3 of FIG. 6). Ina third example, the allocation logic 412 may determine to structure theexternal memory allocation using one or more logical relationships, suchas striping with parity, between multiple regions on multiple memoryappliances. The allocation logic 412 may determine how to structure theexternal memory allocation, using an algorithm or heuristic.

The dynamic allocation of external memory may include a provisioning ofa predetermined amount of memory for the client and/or for a useraccount on the client. One or more subsequent requests to allocateexternal memory for the client and/or the user account may be allocatedfrom the predetermined amount of external memory that was provisionedfor the client and/or for the user account. The request to allocateexternal memory and/or a subsequent request to allocate external memorymay result in allocation of a subset or all of the provisioned externalmemory. The provisioning may be part of the dynamic allocation of theexternal memory. Alternatively or in addition, the provisioning may beseparate from the allocation of the external memory. Thus, allocationmay or may not include the provisioning depending on, for example,whether sufficient external memory has already been provisioned. Theprovisioning of the memory may reserve the memory such that after thememory is reserved for the client, the reserved memory may not beaccessed by other clients unless the reserved memory is freed.Alternatively or in addition, if provisioned to a user account, thereserved memory may not be accessed by other user accounts until thereserved memory is freed.

Provisioning may be the reservation of memory, but alternatively or inaddition, provisioning the external memory may include providing anindication of how to allocate memory, in other words, provisioning mayinclude providing or creating an indication of an allocation strategy.The allocation logic, for example, may use the indication of theallocation strategy to determine the allocation strategy used inallocating memory. The indication of the allocation strategy may becreated by a user logged into a user account, such as an administratoraccount. Alternatively or in addition, the indication of the allocationstrategy may be created by a configuration unit 415 or any other module.The configuration unit may be a component that creates the indication ofthe allocation strategy based on information received through a thirduser interface and/or API. The third user interface may be included, insome examples, in the user interface and/or the second user interfacedescribed above. The third user interface may be a graphical userinterface, a web interface, a command-line interface, an API, and/or anyother type of interface or combination of interfaces known now or laterdiscovered through which data may be received.

The configuration unit 415 may be included in the management server 120as illustrated in FIG. 6. Alternatively or in addition, theconfiguration unit 415 may be included in any other device, such as theclient 130 or the memory appliance 110.

The indication of the allocation strategy may include one or more stepsand/or rules that the allocation logic follows to determine how toallocate external memory. Determining how to allocate external memory,for example, may include identifying the memory appliances on which toallocate requested memory. Alternatively, or in addition, the indicationof the allocation strategy may include profiles for memory appliances,clients, and/or user accounts. The profiles may indicate to theallocation logic how to allocate the memory.

Creating or providing the indication of the allocation strategy may beprovisioning external memory for one or more of the clients, for one ormore user accounts, and/or for predetermined purposes. In a firstexample, creating the indication of the allocation strategy may includeassociating a user account with a high priority setting. Creating suchan association may provision external memory for use by the user accountfrom a set of the memory appliances that are configured to be used byany high priority user accounts. In a second example, creating theindication of the allocation strategy may include setting a time limitfor a user account, such as a time-of-day limit or a duration-of-uselimit. Setting the time limit may provision external memory for use bythe user account only during predetermined times, such as during apredetermined time of day or during predetermined days of a week, oronly for a predetermined length of time. In a third example, creatingthe indication of the allocation strategy may include setting a maximumexternal memory usage limit for a user account, thus limiting the amountof external memory that may be allocated to the third user account. In afourth example, creating the indication of the allocation strategy mayinclude creating one or more steps and/or rules that indicate theallocation logic is to prefer to allocate memory on the memoryappliances having low network bandwidth when satisfying requests fromthe clients that have low network bandwidth. In other words, low networkbandwidth clients may be provisioned with low network bandwidth externalmemory and/or lower speed external memory. The client profile, forexample, may indicate that the client is a low network bandwidth client.In a fifth example, creating the indication of the allocation strategymay include identifying one or more steps and/or rules that indicate theallocation logic is to prefer to allocate memory on the memoryappliances that have a network locality near to the clients. In otherwords, external memory may be provisioned to the clients with a networklocality within a threshold distance of the memory appliances thatcontain the provisioned memory. Other examples of provisioning mayinclude configuring the allocation logic to execute any of the othersteps/rules described elsewhere in this document. Provisioning externalmemory may include configuring any of the characteristics and/orconfigurations of the memory appliance, the client, and/or the useraccount described elsewhere in this document on which the allocationlogic determines how to allocate memory. The steps and/or rules to usemay be configured for each memory appliance, for each client, and/or foreach user account. Alternatively or in addition, the steps and/or rulesto use may be configured globally for all memory appliances, clients,and/or user accounts. The steps and/or rules to use may be configuredwith relative priorities to each other, such as by ranking the stepsand/or rules in order of precedence. All or part of the profiles may bedetermined and/or identified by the allocation logic. For example, theallocation logic may auto-detect that the client and/or the memoryappliance has low network bandwidth by measuring performance and/or byretrieving information indicating performance.

The allocation logic 412 may include one or more steps and/or rules todetermine which memory appliances to use or select for a particularexternal memory allocation. The allocation logic 412 may determine thememory appliances based on factors such as, how much memory to use oneach memory appliance, which one or more logical relationship types touse if any, which restrictions to place upon the external memoryallocation if any, and/or whether to reject the request. For example,the allocation logic 412 may use memory appliances that are associatedwith the management server 120 and/or known to the allocation logic 412of the management server 120. Alternatively, or in addition, theallocation logic 412 may determine the memory appliances to use based ona profile that includes one or more of the characteristics and/orconfigurations of the memory appliances.

In a first example, the allocation logic 412 may use or select memoryappliances that have the least amount of available memory while stillhaving enough to hold the entire external memory allocation in a singleregion. In a second example, the allocation logic 412 may use or selectmemory appliances that have network locality near to the client 130. Ina third example, the allocation logic 412 may use or select memoryappliances that have a backing store. In a fourth example, theallocation logic 412 may use or select memory appliances that have lownetwork utilization. In a fifth example, the allocation logic 412 mayuse or select memory appliances that have low latency for client-sidememory access. In a further example, the allocation logic 412 may use orselect memory appliances that have high bandwidth for client-side memoryaccess.

Alternatively, or in addition, the allocation logic 412 may utilize aprofile that includes one or more characteristics and/or configurationsof the client 130 and/or of a user account. In addition to those listedelsewhere in this disclosure, characteristics and/or configurations ofthe client 130 and/or of the user account may include, for example:relative priority, absolute priority, quotas, maximum external memoryusage limits, current external memory usage, maximum persistent externalmemory usage limits, current persistent external memory usage, maximumvolatile external memory usage limits, current volatile external memoryusage, time-of-day limits, duration-of-use limits, last access time,maximum allowed not-in-use threshold, and/or any other propertiesdescribing the capabilities of, actions of, and/or privileges assignedto, the client 130 and/or the user account. In a first example, theallocation logic 412 may use or select memory appliances with olderhardware revisions for user accounts with low relative priority. In asecond example, the allocation logic 412 may use or select memoryappliances with low latency for client-side memory access for clientswith high absolute priority. In a third example, the allocation logic412 may reject a request to create an external memory allocation outsidea time-of-day limit for the user account. In a further example, theallocation logic 412 may prefer to use or select memory appliances withlow network bandwidth for clients with low network bandwidth. In a fifthexample, the allocation logic 412 may assign a short lease time for useraccounts with a short duration-of-use limit.

Alternatively, or in addition, a separate module, other than theallocation logic 412 may be included in the management server 120 todetermine the distribution of the external memory across the memoryappliances. Alternatively, or in addition, the distribution may bedetermined by the client logic 312 and/or the region access logic 212.Alternatively, or in addition, the determination of the distribution ofthe regions of the external memory allocation may be distributed betweenmultiple logics, such as the client logic 312 and the allocation logic412. All of, or a portion of, the steps performed for the determinationmay be included in the request to create an external memory allocationor in any other message or data sent from the client logic 312 to theallocation logic 412. Alternatively or in addition, the request tocreate an external memory allocation may include an indication of whichfactors to use to determine how to structure the external memoryallocation. Alternatively or in addition, the request to create anexternal memory allocation may include parameters to be used whendetermining the structure of the external memory allocation. Forexample, the parameters may include one or more physical locations to beused when choosing memory appliances based upon physical locations.Alternatively, or in addition, the parameters may include informationdescribing the user account and/or access parameters to be used whenchoosing memory appliances based upon user accounts. Alternatively, orin addition, the user account and/or access parameters may be specifiedat the time a connection, such as an SSL connection, is establishedbetween the client logic 312 and the allocation logic 412.

FIG. 7 illustrates an example flowchart for creation of an externalmemory allocation. The request to create an external memory allocationmay include additional parameters that the allocation logic 412 may useto affect the external memory allocation, the regions, the logicalrelationships between the regions, and/or a combination of these (702,704). In a first example, the request to create an external memoryallocation may include a size to use for the external memory allocation.In a second example, the request to create the external memoryallocation may include a preferred external memory allocationidentifier. The preferred external memory allocation identifier mayrefer to an existing external memory allocation. If an existing externalmemory allocation referenced by the preferred external memory allocationidentifier exists, the allocation logic 412 may select the existingexternal memory allocation instead of creating a new external memoryallocation (706, 710). The allocation logic 412 may perform additionalchecks before selecting an existing external memory allocation, such asconfirming that the other parameters specified in the request to createan external memory allocation match the existing external memoryallocation (710). Upon selecting an existing external memory allocation,if the regions referenced by the existing external memory allocation arenot included in the memories of the corresponding memory appliances, theallocation logic 412 may send a request to restore the contents of aregion from a backing store for each region referenced by the existingexternal memory allocation (712, 714). Alternatively, or in addition,the request to create an external memory allocation may include anindicator that only existing external memory allocations may beconsidered when attempting to satisfy the request. If no existingexternal memory allocations match the parameters indicated in therequest to create an external memory allocation, then the request tocreate an external memory allocation may fail (780). Alternatively, theallocation logic 412 may reconfigure existing regions by sending regionreconfiguration requests to the region access logic 212 of the memoryappliances including the existing regions (716). For example, theallocation logic 412 may request the region access logic 212 to resizethe existing regions, or revise other parameters such as the accessparameters associated with the existing region. In case reconfigurationof the existing region fails, the external memory allocation may fail(780). In another example, if the request for external memory allocationindicates, such as using parameters, a preference not to usereconfigured regions, the request may fail (716, 780). Alternatively,the allocation logic 412 may proceed to request creation of memoryregions instead of the request failing (720). In a third example, therequest to create an external memory allocation may include anallocation type. The allocation type may indicate how the allocationlogic 412 and/or the region access logic 212 may treat the externalmemory allocation after it is created.

In a first example, the allocation type may indicate that the externalmemory allocation may be treated as volatile. A volatile external memoryallocation may be destroyed if the allocation logic 412 determines thatthe external memory allocation is no longer in use. As such, a clientlogic 312 may avoid memory leaks by specifying that its external memoryallocation may be treated as volatile, since a failure of the client130, the client logic 312, and/or the application logic 314 mayeventually lead to the allocation logic 412 determining that theexternal memory allocation is no longer in use, then destroying it.

The allocation logic 412 may determine whether or not an external memoryallocation is in use by requesting and/or inspecting the status of theexternal memory allocation and/or of the regions referenced by theexternal memory allocation. The status may include an indication of howmany clients are accessing the external memory allocation and/or theregions referenced by the external memory allocation. Alternatively, orin addition, the status may include an indication of the last time atwhich a client accessed the external memory allocation and/or theregions referenced by the external memory allocation. The allocationlogic 412 may determine that the external memory allocation is not inuse if the status indicates the last time at which a client accessed theexternal memory allocation and/or the regions referenced by the externalmemory allocation was older than a not-in-use threshold. The not-in-usethreshold may be a parameter of the request to create an external memoryallocation. Alternatively, or in addition, the not-in-use threshold maybe specified by an administrator using the user interface.Alternatively, or in addition, the not-in-use threshold may bedetermined automatically, such as based-upon an algorithm, a heuristic,and/or a formula. An example algorithm, heuristic, and/or formula mayadjust the not-in-use threshold based upon the characteristics and/orconfiguration of the management server 120 and/or of the memoryappliances 110 a-110 c, such as the amount of available memory.Alternatively, or in addition, the allocation logic 412 may determinewhether or not an external memory allocation is in use by inspectingregion metadata 215 and/or external memory allocation metadata 414, ifeither or both are included in the management server 120. Regionmetadata may include an indication of the last time at which a clientaccessed the region. External memory allocation metadata 414 may includean indication of the last time at which a client accessed the externalmemory allocation.

In a second example, the allocation type may indicate that the externalmemory allocation may be treated as persistent. A persistent externalmemory allocation may be preserved if the allocation logic 412determines that the external memory allocation is no longer in use. Apersistent external memory allocation may be preserved by enabling theexternal memory allocation and/or the regions referenced by the externalmemory allocation to continue to exist as created. Alternatively, or inaddition, if the allocation logic 412 determines that the externalmemory allocation is no longer in use, the allocation logic 412 and/orthe region access logic 212 may automatically persist the externalmemory allocation and/or the regions referenced by the external memoryallocation to the backing stores and remove one or both from memory. Assuch, the client logic 312 may avoid memory leaks by specifying that itsexternal memory allocation may be treated as persistent with anot-in-use threshold, since a failure of the client 130, the clientlogic 312, and/or the application logic 314 may eventually lead to theallocation logic 412 determining that the external memory allocation isno longer in use, then persisting it and removing it from memory. Theallocation logic 412 updates the external memory allocation metadataaccording to the allocation type specified (730).

The allocation logic 412 may also associate an external memoryidentifier with the external memory allocation metadata (730). Theexternal memory identifier may be chosen by the allocation logic 412 orit may be included in the request to create an external memoryallocation. For example, the external memory identifier may be thepreferred external memory identifier included in the request to createan external memory allocation.

The allocation logic 412 may send a request to create a region to theregion access logic 212 of each memory appliance selected to hold memoryregions referenced by the external memory allocation (720, 722, 724).The memory appliances are selected as described earlier. Upon receivingthe response message in response to each request to create a region, theallocation logic 412 may inspect the response message and/or record anyrelevant metadata (728). In case any of the region allocation requestsfail, the creation of the external memory allocation may fail (780).

The allocation logic 412 may respond to the request to create anexternal memory allocation with a response message. The response messagemay include the external memory identifier. Alternatively, or inaddition, the response message may include identifiers and/orinformation describing the regions referenced by the external memoryallocation and/or the logical relationships between the regions.Alternatively, or in addition, the response message may include astatus, indicating whether the operation was successful (790, 740, 780).

Upon receiving a request to resize an existing external memoryallocation, the allocation logic 412 may determine how to structure theresized external memory allocation. In a first example, the allocationlogic 412 may determine to structure the resized external memoryallocation as a single region on a single memory appliance. In a secondexample, the allocation logic 412 may determine to structure theexternal memory allocation as multiple regions on multiple memoryappliances. In a third example, the allocation logic 412 may determineto structure the external memory allocation using one or more logicalrelationships, such as striping with parity, between multiple regions onmultiple memory appliances. Determining how to structure the resizedexternal memory allocation may include determining whether to resize theexisting regions referenced by the external memory allocation, whetherto create additional regions, and/or whether to replace existing regionswith new regions.

The allocation logic 412 may determine how to structure the resizedexternal memory allocation. As additional examples to those listedelsewhere in this disclosure, the allocation logic 412 may resizeexisting regions when expanding or contracting an external memoryallocation that only references one region, if sufficient space isavailable in the memory of the memory appliance including the region. Inanother example, the allocation logic 412 may create additional regionswhen expanding an external memory allocation that uses a logicalrelationship involving a concatenation of the regions referenced by theexternal memory allocation. In another example, the allocation logic 412may resize existing regions when expanding or contracting an externalmemory allocation that uses a logical relationship involving stripingand/or mirroring, if sufficient space is available in the memory of thememory appliances including the regions referenced by the externalmemory allocation.

The allocation logic 412 may create additional regions by sending arequest to create an external memory allocation to the region accesslogic 212 of the memory appliances selected to include the additionalregions. Alternatively, or in addition, the allocation logic 412 mayresize existing regions by sending a request to resize an existingregion to the region access logic 212 of the memory appliances includingthe existing regions. Alternatively, or in addition, the allocationlogic 412 may destroy existing regions by sending a request to destroy aregion to the region access logic 212 of the memory appliances includingthe existing regions.

The allocation logic 412 may replace an existing region with a newregion by creating the new region, then replicating the data from theexisting region onto the new region. For example, the allocation logic412 may perform client-side memory access to read the data from theexisting region and write to the new region. Alternatively, or inaddition, the allocation logic 412 may send a request to migrate aregion to the region access logic 212 of the memory appliance includingthe existing region and/or to the region access logic 212 of the memoryappliance selected to include the new region.

The allocation logic 412 may respond to the request to resize anexisting external memory allocation with a response message. Theresponse message may include the external memory identifier.Alternatively, or in addition, the response message may includeidentifiers and/or information describing the regions referenced by theexternal memory allocation and/or the logical relationships between theregions. Alternatively, or in addition, the response message may includea status, indicating whether the operation was successful.

Upon receiving a request to renew an external memory allocation, theallocation logic 412 may update the external memory allocation metadata414 associated with the external memory allocation identified by therequest. The request to renew an external memory allocation may includean external memory allocation identifier. Alternatively, or in addition,the request to renew an external memory allocation may include a valueto be used for the not-in-use threshold of the external memoryallocation. The allocation logic 412 may respond to the request to renewan external memory allocation with a response message. The responsemessage may include a status, indicating whether the operation wassuccessful. Alternatively, or in addition, the response message mayinclude the not-in-use threshold of the external memory allocationand/or the time left until the external memory allocation may beconsidered not-in-use.

Upon receiving a request to destroy an external memory allocation, theallocation logic 412 may send to the region access logic 212 of eachcorresponding memory appliance, a request to destroy a region for eachregion referenced by the external memory allocation. Upon receiving theresponse message in response to each request to destroy a region, theallocation logic 412 may inspect the response message and/or record anyrelevant metadata. The allocation logic 412 may respond to the requestto destroy an external memory allocation with a response message. Theresponse message may include a status, indicating whether the operationwas successful.

Upon receiving a request to persist and free an existing external memoryallocation, the allocation logic 412 may, for each region referenced bythe external memory allocation, send to the region access logic 212 ofeach corresponding memory appliance, a request to persist a region to abacking store and remove it from memory. Upon receiving the responsemessage in response to each request to persist a region to a backingstore and remove it from memory, the allocation logic 412 may inspectthe response message and/or record any relevant metadata 414. Theallocation logic 412 may respond to the request to persist and free anexisting external memory allocation with a response message. Theresponse message may include a status, indicating whether the operationwas successful.

Upon receiving a request to list existing external memory allocations,the allocation logic 412 may respond with a response message. Theresponse message may include a list of external memory allocationidentifiers for the external memory allocations associated with themanagement server 120. For example, in case of the system as illustratedin FIG. 6, the management server 120 may provide a list containinginformation of the external memory allocations X1-X3. Alternatively, orin addition, the response message may include a status, indicatingwhether the operation was successful.

Upon receiving a request to get information regarding an external memoryallocation, the allocation logic 412 may respond with a responsemessage. The response message may include the external memoryidentifier. Alternatively, or in addition, the response message mayinclude identifiers and/or information describing the regions referencedby the external memory allocation and/or the logical relationshipsbetween the regions.

For example, in case the allocation logic 412 of the management server120 of FIG. 6 receives a request to get information regarding theexternal memory allocation X1, the allocation logic 412 may retrieveregion metadata 215 a-c by sending a request to get information for theregions R1-R3 referenced by X1. The requests may be sent to the regionaccess logic 212 a-212 c included in the memory appliances 110 a-110 cincluding the regions R1-R3. The identifiers and/or information mayinclude access parameters for the regions, such as a password and/or anencryption key. Alternatively, or in addition, the response message mayinclude metadata describing the external memory allocation X1, such asthe not-in-use threshold for the external memory allocation X1 and/orfor the regions R1-R3. Alternatively, or in addition, the responsemessage may include a status, indicating whether the operation wassuccessful.

Upon receiving a request to restructure an external memory allocation,the allocation logic 412 may determine how to structure the externalmemory allocation. The allocation logic 412 may determine how tostructure the external memory allocation as described elsewhere in thisdisclosure. Alternatively, or in addition, the request to restructure anexternal memory allocation may include parameters specifying a desiredstructure for the external memory allocation and/or specifyingparameters to be used to determine a revised structure. For example, theparameters may cause the allocation logic 412 to use a logicalrelationship involving striping between the regions referenced by theexternal memory allocation. Alternatively, or in addition, theparameters may cause the allocation logic 412 to use memory applianceswith higher or lower bandwidth than the memory appliances including theregions currently referenced by the external memory allocation.Alternatively, or in addition, the parameters may cause the allocationlogic 412 to use memory appliances that are closer to or farther from aspecified physical and/or network location than the memory appliancesincluding the regions currently referenced by the external memoryallocation. As such, a request to restructure an external memoryallocation may be used to migrate data closer to or further away fromthe client 130, for increasing or decreasing locality and/or forincreasing or decreasing performance. This migrating of data may be partof a broader approach for balancing the cost/performance of memoryincluded in the client 130, memory included in the memory appliances,and/or other media capable of holding the data, such as the backingstore or other backing stores. Determining how to structure the externalmemory allocation may include determining whether to resize the existingregions referenced by the external memory allocation, whether to createadditional regions, and/or whether to replace existing regions with newregions. The allocation logic 412 may resize the existing regionsreferenced by the external memory allocation, create additional regions,and/or replace existing regions with new regions using the methodsdescribed throughout this disclosure.

Using information provided by the allocation logic 412, by the regionaccess logic 212, or both, the client logic may access one or moreregions using client-side memory access. The client 130 may present adata interface to the application logic 314. The data interface may takemany forms and/or may depend upon the preferences of the applicationlogic 314 and/or of the users. Some examples of data interfaces mayinclude: an API, block-level interface, a character-level interface, amemory-mapped interface, a memory allocation interface, a memoryswapping interface, a memory caching interface, a hardware-accessibleinterface, a graphics processing unit (GPU) accessible interface and/orany other interface used to access the data and/or metadata of thememory appliance 110, the management server 120, the region 214, theexternal memory allocation, and/or the regions referenced by theexternal memory allocation. Alternatively or in addition, the datainterface may include multiple interfaces. The data interface may be adata interface unit. The functionality of any of the data interfaces maybe provided using all of or a portion of the functionality of any one ormore of the other data interfaces. For example, a block-level interfacemay use methods of an API in order to retrieve and/or manipulateexternal memory allocations and/or the regions referenced by an externalmemory allocation. Alternatively, or in addition, an API may includemethods to manipulate a block device interface.

In a first example, the data interface may include an API. An API mayprovide methods for the application logic 314 to invoke that manipulatea region. The methods for the application logic 314 to invoke thatmanipulate a region may include methods that manipulate data included inthe region, methods that manipulate the metadata associated with theregion, methods that manipulate the access controls for the region,and/or any other methods related to the region. For example, a methodmay enable the application logic 314 to read or write data to a specificlocation within the region. Alternatively, or in addition, an API mayprovide methods for the application logic 314 to invoke that manipulatean external memory allocation. The methods for the application logic 314to invoke that manipulate an external memory allocation may includemethods that manipulate data included in the regions referenced by theexternal memory allocation, methods that manipulate the metadataassociated with the regions, methods that manipulate the metadataassociated with the logical relationships between the regions, methodsthat manipulate the metadata associated with the external memoryallocation, methods that manipulate the access controls for the regions,methods that manipulate the access controls for the external memoryallocation, and/or any other methods related to the external memoryallocation, the logical relationships between the regions, and/or theregions referenced by the external memory allocation. In an example, amethod may enable the application logic 314 to read or write data to aspecific location within the external memory allocation. Reading datafrom a first location within an external memory allocation may causedata to be read from one or more second locations within one or moreregions referenced by the external memory allocation. Writing data to afirst location within an external memory allocation may cause data to bewritten to one or more second locations within one or more regionsreferenced by the external memory allocation. The second locations andthe regions may be determined based upon the logical relationshipsbetween the regions. In a second example, a method may enable theapplication logic 314 to run a consistency check upon an external memoryallocation that uses a parity-based logical relationship. In a thirdexample, a method may facilitate the application logic 314 to registerthe memory of the client and/or a portion of the memory with one or morecommunication interfaces. Registering memory may cause subsequentclient-side memory access operations using the registered memory toproceed more quickly and/or more efficiently than operations not usingthe registered memory.

Alternatively, or in addition, an API may provide methods for theapplication logic 314 to invoke that retrieve, present, and/ormanipulate information related to the management servers, the memoryappliance, the external memory allocations, the regions referenced bythe external memory allocations, and/or the logical relationshipsbetween the regions. The methods may provide functionality similar tothe allocation logic requests and/or region access logic requests.Alternatively, or in addition, the methods may provide functionalitysimilar to a combination of one or more of the allocation logic requestsand/or region access logic requests. In a first example, an API mayprovide methods for the application logic 314 to retrieve a list ofmanagement servers. In a second example, an API may provide methods forthe application logic 314 to retrieve a list of memory appliances, suchas the memory appliances associated with a management server and/orknown by the allocation logic of a management server. In a thirdexample, an API may provide methods for the application logic 314 toretrieve a list of external memory allocations, such as the externalmemory allocations associated with a management server. In a fourthexample, an API may provide methods for the application logic 314 toretrieve a list of regions, such as the regions included in the memoryof a memory appliance or the regions associated with an external memoryallocation. In a fifth example, an API may provide methods for theapplication logic 314 to retrieve information related to an externalmemory allocation, such as the size of the external memory allocation,the regions referenced by the external memory allocation, and/or thelogical relationships between the regions. In a fifth example, an APImay provide methods for the application logic 314 to manipulate anexternal memory allocation. An API may manipulate the external memoryallocation using the allocation logic requests and/or the region accesslogic requests. In a sixth example, an API may provide methods for theapplication logic 314 to manipulate a region. An API may manipulate aregion using the region access logic requests.

In a second example, the data interface may include a block-levelinterface. The block-level interface may provide block-level access todata of a region. Alternatively or in addition, the block-levelinterface may provide block-level access to data of one or more of theregions referenced by an external memory allocation. Alternatively or inaddition, the block-level interface may provide block-level access todata of the external memory allocation. Block-level access to data mayinclude reading data from or writing data to a consistently-sized and/oraligned portion of a region or an external memory allocation. The clientlogic may provide block-level access using a block device interface.Alternatively, or in addition, the client logic may provide block-levelaccess using any storage protocol now known or later discovered. Astorage protocol may be any communications protocol used to transferdata between a block storage device, interface, or system, such as theblock-level interface or any other data interface, and a device orsystem, such as the client or another client, that stores data in,and/or retrieves data from, the block storage device, interface, orsystem. A storage protocol may be implemented, for example, using one ormore software and/or hardware storage controllers. The storage protocoland electrical characteristics of the hardware storage controller may bepart of a common standard. In one example, the storage protocol may bethe universal serial bus mass storage device class (USB MSC or UMS),which is a set of computing communications protocols defined by the USBImplementers Forum that runs on a hardware bus, such as the one or moreinterconnects, that conforms to the USB standard. In a second example,the storage protocol may be the Small Computer System Interface (SCSI)command protocol. In a third example, the storage protocol may be theSerial Advanced Technology Attachment (SATA) protocol. Additionalexamples of the storage protocol include Serial Attached SCSI (SAS) andInternet Small Computer System Interface (iSCSI). Alternatively or inaddition, the block-level interface may provide block-level access usingany storage protocol that transfers data with a data transfer protocol,such as SCSI over Fiber Channel, SCSI RDMA Protocol (SRP) over RemoteDirect Memory Access (RDMA), iSCSI over TCP/IP, or any other combinationof storage protocol and data transfer protocol known now or discoveredin the future. Alternatively, or in addition, the block-level interfacemay provide block-level access by emulating the storage protocol and/ordata transfer protocol. In one example, the block-level interface mayprovide block-level access by providing a SCSI command interface to theapplication logic. In a second example, the block-level interface mayprovide block-level access using a storage protocol with an emulateddata transfer protocol, such as with a virtualized communicationinterface.

In a third example, the data interface may include a character-levelinterface. The character-level interface may provide character-leveland/or byte-level access to data of a region. Alternatively or inaddition, the character-level interface may provide character-leveland/or byte-level access to data of one or more of the regionsreferenced by an external memory allocation. Alternatively or inaddition, the character-level interface may provide character-leveland/or byte-level access to data of the external memory allocation. Theclient logic may provide character-level access using a character deviceinterface. Character-level access may enable the application logic 314to read and/or write to character-aligned portions of the externalmemory allocation or of the regions referenced by the external memoryallocation. Byte-level access may enable the application logic 314 toread and/or write to byte-aligned portions of the external memoryallocation or of the regions referenced by the external memoryallocation. Alternatively or in addition, the character-level interfacemay enable the application logic 314 to seek to a specified locationwithin the external memory allocation or the regions referenced by theexternal memory allocation. Seeking to a specified location may causesubsequent attempts to read and/or write to the external memoryallocation or the regions referenced by the external memory allocationto start at the most recently seeked-to location. Alternatively, or inaddition, attempts to read and/or write to the external memoryallocation or the regions referenced by the external memory allocationmay start at a location after the most recently read and/or writtenportion.

In a fourth example, the data interface may include a memory-mappedinterface. The memory mapped interface may enable the application logic314 to map all of or a portion of a region, an external memoryallocation and/or of one or more regions referenced by the externalmemory allocation into a virtual address space, such as the virtualaddress space of the application logic. The memory-mapped interface mayinclude an API. Alternatively, or in addition, the memory-mappedinterface may include and/or utilize a block-level interface and/or acharacter-level interface. In one example, the memory-mapped interfacemay enable the application logic 314 to map all of or a portion of ablock device interface into a virtual address space, such as the virtualaddress space of the application logic.

The memory mapped interface may include a page fault handler method. Thepage fault handler method may be executed when the application logicattempts to access a first portion of the virtual address space. Thefirst portion may be configured to trigger the page fault handler whenaccessed. The first portion may be a page of the virtual address space.Alternatively, or in addition, the first portion may be included in themapped portion of the virtual address space. The page fault handler mayperform client-side memory access to read a second portion of theexternal memory allocation and/or of one or more regions referenced bythe external memory allocation into a third portion of the memory of theclient. The third portion may be a page of the memory of the client.Alternatively, or in addition, the page fault handler may allocate thethird portion of the memory of the client 130. The page fault handlermay map the first portion of the virtual address space to the thirdportion of the memory. The first portion may correspond to the secondportion. For example, the offset of the first portion within the mappedportion of the virtual address space may equal the offset of the secondportion within the external memory allocation or the regions referencedby the external memory allocation. Alternatively, or in addition, thesecond portion may include a fourth portion corresponding to the thirdportion. The portion of the second portion not included in the fourthportion may be considered a fifth portion. For example, the page faulthandler method may determine based upon a pattern of calls to the pagefault handler method that the fifth portion of the external memoryallocation and/or of the one or more regions may be needed soon andtherefore, may be read into the memory in anticipation, such as with aread-ahead predicting algorithm.

Alternatively, or in addition, the memory mapped interface may include abackground process. The background process may periodically flush dirtypages. Flushing dirty pages may include performing client-side memoryaccess to write the data from the dirty pages to the correspondinglocations within the external memory allocation and/or the one or moreregions referenced by the external memory allocation. Dirty pages may bepages included in the memory of the client which have been written to bythe application logic 314 and/or the client logic 312 since they werelast read from or written to the external memory allocation and/or theone or more regions referenced by the external memory allocation.

Alternatively, or in addition, the memory mapped interface may include apage evicting method. Pages to be evicted may include the one or morepages of the memory used to hold the third portion of the memory of theclient. The page evicting method may be executed when the memory-mappedinterface determines that the pages to be evicted are unlikely to beaccessed again soon, when the memory-mapped interface determines thatthe pages to be evicted are needed to hold data for other executions ofthe page fault handler method, and/or when the pages to be evicted areneeded to hold data for any other purpose. If one or more of the pagesto be evicted are dirty pages, the page evicting method may performclient-side memory access to write data from the dirty pages to acorresponding portion of the external memory allocation and/or theregions referenced by the external memory allocation. The page evictingmethod may update metadata to indicate that the pages to be evicted maybe re-used for other purposes, such as by the page fault handler method.

In a fifth example, the data interface may include a memory allocationinterface. The memory allocation interface may include an API. Thememory allocation interface may include one or more methods that enablethe application logic 314 to allocate individual buffers. For example,an application may allocate a buffer to hold an integer, an array ofintegers, a character, a string, and/or any other data. Alternatively,or in addition, the memory allocation interface may include one or moremethods that enable an application-level memory allocator to allocateslabs of memory. A slab of memory may include one or more pages. The oneor more pages included in the slab may be contiguous in a physicaladdress space and/or in a virtual address space. A slab of memory may befurther sub-divided by the application-level memory allocator. Forexample, the application-level memory allocator may enable theapplication logic 314 to allocate individual buffers from portions ofthe slab of memory. The memory allocation interface may utilize amemory-mapped interface. For example, allocating the individual buffersand/or allocating the slabs of memory may include mapping all of or aportion of an external memory allocation and/or of one or more regionsreferenced by the external memory allocation into a virtual addressspace, such as the virtual address space of the application. The virtualaddress of an individual buffer and/or of a slab may be included in aportion of the virtual address space corresponding to a portion of theexternal memory allocation and/or of the regions. Alternatively, or inaddition, allocating the individual buffers and/or allocating the slabsof memory may include creating one or more external memory allocationsand/or regions. The memory allocation interface may be made availableselectively to one or more application logics. Alternatively, or inaddition, the memory allocation interface may be made available to allapplication logics.

In a sixth example, the data interface may include a memory swappinginterface. The memory swapping interface may include an API. The memoryswapping interface may enable the application logic 314 to removeinfrequently accessed data from primary memory. In one exampleimplementation, the application logic 314 may be an operating system, ora portion of an operating system, such as a kernel and/or a memorymanagement subsystem. The memory swapping interface may include ablock-level interface. The memory swapping interface may include a swapdevice. Alternatively, or in addition, the memory swapping interface mayinclude a character-level interface. For example, the memory swappinginterface may emulate a swap file using a character device interfaceand/or a block device interface. The memory swapping interface may bemade available to all applications in the client 130, such as theapplication logic 314, or to a subset of applications. The memoryswapping interface may include a transcendental memory interface. Forexample, the memory swapping interface may include a front-swapinterface. The front-swap interface may include one or more methods toinitialize the front-swap interface, to store a page, to get a page, toinvalidate a page, and/or to invalidate multiple pages.

A method to initialize the front-swap interface may initialize metadata.The metadata may include offsets within the external memory allocationsand/or the regions for where to find the data from zero or more pages.The metadata may include one or more data structures to facilitate fastlookup of the offsets. For example, the metadata may include a hashtable, a red-black tree, a radix tree, and/or any other data structureknown now or later discovered. The one or more data structures may beindexed and/or may include an index based upon an identifier for thezero or more pages. The metadata may be included in the memory of theclient. Alternatively, or in addition, the metadata may be included inthe external memory allocations, regions referenced by the externalmemory allocations, in the region metadata 215, and/or in the externalallocation metadata 318.

A method to store a page may perform client-side memory access to writedata from the page to a corresponding portion of one or more externalmemory allocations and/or one or more regions referenced by the one orexternal memory allocations. Alternatively, or in addition, the methodto store a page may update metadata indicating the presence and/oroffset of the data from the page in the external memory allocationsand/or the regions. The method to store a page may perform client-sidememory access to read and/or write the metadata from/to a locationwithin the external memory allocations and/or regions referenced by theexternal memory allocations.

A method to get a page may perform client-side memory access to readdata into the page from a corresponding portion of the external memoryallocations and/or the regions referenced by the external memoryallocations. The method to get a page may utilize the metadata and/orthe one or more data structures to determine the offset for where tofind the data from the page. The method to get a page may performclient-side memory access to read and/or write the metadata from/to alocation within the external memory allocations and/or regionsreferenced by the external memory allocations.

A method to invalidate a page may update metadata indicating thenon-presence of the data from the page in the external memoryallocations and/or the regions. Updating the metadata may includeupdating the one or more data structures. The method to invalidate apage may perform client-side memory access to read and/or write themetadata from/to a location within the external memory allocationsand/or regions referenced by the external memory allocations.Alternatively, or in addition, the method to invalidate a page mayperform client-side memory access to overwrite data from the page to acorresponding portion of the external memory allocations and/or theregions referenced by the external memory allocations.

A method to invalidate multiple pages may update metadata indicating thenon-presence of the data from the multiple pages in the external memoryallocation and/or the regions. The multiple pages may be all pagesassociated with a specified swap area, swap device, swap partition,and/or swap file. Updating the metadata may include updating the one ormore data structures. For example, updating the metadata may includeemptying and/or removing one or more data structures. The method toinvalidate a page may perform client-side memory access to read and/orwrite the metadata from/to a location within the external memoryallocations and/or regions referenced by the external memoryallocations. Alternatively, or in addition, the method to invalidatemultiple pages may perform client-side memory access to overwrite datafrom the multiple pages to one or more corresponding portions of theexternal memory allocations and/or the regions referenced by theexternal memory allocations.

In a seventh example, the data interface may include a memory cachinginterface. The memory caching interface may include an API. The memorycaching interface may enable the application logic 314 to store datafrom secondary memory in external memory. For example, the memorycaching interface may store data from secondary memory in regions, in anexternal memory allocation, and/or in the regions referenced by theexternal memory allocation. In one example implementation, theapplication logic 314 may be an operating system, or a portion of anoperating system, such as a kernel and/or a page cache subsystem. Datafrom secondary memory may include data from a block-level interface,from a block device interface, from a file system, and/or from any otherform of secondary memory. In one example, data from secondary memory mayinclude pages of data from a file system. The memory caching interfacemay be made available to all applications in the client 130, such as theapplication logic 314. The memory caching interface may include apage-caching interface. Alternatively, or in addition, the memory mayinclude a transcendental memory interface. For example, the memorycaching interface may include a clean-cache interface. The clean-cacheinterface may include one or more methods to initialize a file systemcache, to put a page, to get a page, to invalidate a page, and/or toinvalidate multiple pages.

A method to initialize a file system cache may initialize metadata. Themetadata may include offsets within the external memory allocationsand/or the regions for where to find the data from zero or more pages.The metadata may include one or more data structures to facilitate fastlookup of the offsets. For example, the metadata may include a hashtable, a red-black tree, a radix tree, and/or any other data structureknown now or later discovered. The one or more data structures may beindexed and/or may include an index based upon an identifier for thezero or more pages, an identifier for the file system, an identifier fora file system object, any other identifier relevant to the data beingstored in external memory, and/or a combination of multiple identifiers,such as a concatenation and/or hash of identifiers. The file systemobject may be an inode, a file, a directory, and/or any otherrepresentation of data in a file system. The metadata may be included inthe memory of the client 130. Alternatively, or in addition, themetadata may be included in the external memory allocations, regionsreferenced by the external memory allocations, in the region metadata,and/or in the external allocation metadata. Alternatively, or inaddition, a method to initialize a file system cache may initialize afile system cache for a shared and/or clustered file system.Alternatively, or in addition, the memory caching interface may includea separate method to initialize a file system cache for a shared and/orclustered file system.

A method to put a page may perform client-side memory access to writedata from the page to a corresponding portion of one or more externalmemory allocations and/or one or more regions referenced by the one ormore external memory allocations. Alternatively, or in addition, themethod to put a page may update metadata indicating the presence and/oroffset of the data from the page in the external memory allocationsand/or the regions. The method to put a page may perform client-sidememory access to read and/or write the metadata from/to a locationwithin the external memory allocations and/or regions referenced by theexternal memory allocations.

A method to get a page may perform client-side memory access to readdata into the page from a corresponding portion of the external memoryallocations and/or the regions referenced by the external memoryallocations. The method to get a page may utilize the metadata and/orthe one or more data structures to determine the offset for where tofind the data from the page. The method to get a page may performclient-side memory access to read and/or write the metadata from/to alocation within the external memory allocations and/or regionsreferenced by the external memory allocations.

A method to invalidate a page may update metadata indicating thenon-presence of the data from the page in the external memoryallocations and/or the regions. Updating the metadata may includeupdating the one or more data structures. The method to invalidate apage may perform client-side memory access to read and/or write themetadata from/to a location within the external memory allocationsand/or regions referenced by the external memory allocations.Alternatively, or in addition, the method to invalidate a page mayperform client-side memory access to overwrite data from the page to acorresponding portion of the external memory allocations and/or theregions referenced by the external memory allocations.

A method to invalidate multiple pages may update metadata indicating thenon-presence of the data from the multiple pages in the external memoryallocation and/or the regions. The multiple pages may be all pagesassociated with a specified block device interface, file system, and/orfile system object. Updating the metadata may include updating the oneor more data structures. For example, updating the metadata may includeemptying and/or removing one or more data structures. The method toinvalidate a page may perform client-side memory access to read and/orwrite the metadata from/to a location within the external memoryallocations and/or regions referenced by the external memoryallocations. Alternatively, or in addition, the method to invalidatemultiple pages may perform client-side memory access to overwrite datafrom the multiple pages to one or more corresponding portions of theexternal memory allocations and/or the regions referenced by theexternal memory allocations.

In an eighth example, the data interface may include ahardware-accessible interface. The hardware-accessible interface may bea physically-addressable interface. A physically-addressable interfacemay be an interface which provides access to the underlying data usingphysical addresses, such as the physical addresses used on an addressbus, a CPU interconnect, and/or on a peripheral interconnect. Thehardware-accessible interface may enable a hardware applicationcomponent to access data of a region. Alternatively or in addition, thehardware-accessible interface may enable the hardware applicationcomponent to access data of one or more of the regions referenced by anexternal memory allocation. Alternatively or in addition, thehardware-accessible interface may enable the hardware applicationcomponent to access data of the external memory allocation. The hardwareapplication component may be a processor, a GPU, a communicationinterface, a direct memory access controller, an FPGA, an ASIC, achipset, a hardware logic, and/or any other physical component thataccesses memory. The hardware application component may be included inthe application logic 314. The hardware-accessible interface may includea hardware client component. A hardware client component may be aprocessor, a GPU, an MMU, an IO-MMU, a communication interface, such asthe one or more communication interfaces, an FPGA, an ASIC, a chipset, ahardware logic, a memory access transaction translation logic, any otherhardware component, and/or a combination of multiple hardwarecomponents. The hardware client component may be included in the clientlogic. The hardware client component, the hardware applicationcomponent, and/or the one or more communication interfaces may beembedded in one or more chipsets. The hardware client component mayinclude a memory and/or cache. The memory and/or cache of the hardwareclient component may be used to hold portions of the data of externalmemory allocations and/or regions. Alternatively, or in addition, thehardware client component may utilize a portion of the memory of theclient to hold portions of the data of external memory allocationsand/or regions. The hardware client component may respond to and/ortranslate attempts to access virtual addresses, physical addresses,logical addresses, IO addresses, and/or any other address used toidentify the location of data. Alternatively, or in addition, thehardware client component may participate in a cache coherency protocolwith the hardware application component. In a first example, thehardware client component may respond to attempts of the hardwareapplication component to access physical addresses by accessing dataincluded in the memory and/or cache of the hardware client component. Ina second example, the hardware component may interface with a CPUinterconnect and handle cache fill requests by reading data from thememory and/or cache included in the hardware client component. In athird example, the hardware client component may redirect and/or forwardattempts of the hardware application component to access physicaladdresses to alternate physical addresses, such as the physicaladdresses of the portion of the memory of the client utilized by thehardware component. In a fourth example, the hardware client componentmay translate attempts of the hardware application component to accessphysical addresses into client-side memory access. For example, thehardware client component may interface with the CPU interconnect andhandle cache fill requests by performing client-side memory access toread the requested data from the external memory allocation.Alternatively, or in addition, the hardware client component may handlecache flush requests by performing client-side memory access to writethe requested data to the external memory allocation. Alternatively, orin addition, the hardware client component may handle cache invalidaterequests by updating the memory and/or cache of the hardware clientcomponent to indicate the non-presence of the data indicated by thecache invalidate requests. In a fifth example, the hardware clientcomponent may translate attempts of the hardware application componentto access IO addresses into client-side memory access. For example, thehardware client component may interface with a peripheral interconnect,such as PCI Express, and respond to requests to read a portion of the IOaddress space by reading data from the memory included in the hardwareclient component, by reading the portion of the memory and/or cache ofthe client utilized by the hardware component, and/or by performingclient-side memory access to read the requested data from the externalmemory allocation.

In a ninth example, the data interface may include an interface toenable peripheral devices of the client 130 to access the externalmemory allocations. For example, the data interface may include aGraphics Processing Unit (GPU) accessible interface. The GPU accessibleinterface may enable a GPU application to access data of a region.Alternatively or in addition, the GPU accessible interface may enablethe GPU application to access data of one or more of the regionsreferenced by an external memory allocation. Alternatively or inaddition, the GPU accessible interface may enable the GPU application toaccess data of the external memory allocation. The GPU application maybe an application logic, such as the application logic, executable onone or more processors of a GPU. The GPU may be included in the client.The GPU may include a client-side memory access interface that mayenable the GPU application and/or the GPU accessible interface toperform client-side memory access using the one or more communicationinterfaces included in the client. The client-side memory accessinterface may be a GPUDirect, which is a trademark of NVIDIACorporation, RDMA interface. The GPU accessible interface may includeany one or more data interfaces. The GPU accessible interface mayprovide the one or more data interfaces to the GPU application. Examplesof data interfaces included in the GPU-accessible interface and/orprovided to the GPU application may be: an API, a block-level interface,a character-level interface, a memory-mapped interface, a memoryallocation interface, a memory swapping interface, a memory cachinginterface, a hardware-accessible interface, any other interface used toaccess the data of the external memory allocations and/or of theregions, and/or a combination of data interfaces.

Ownership of and/or access to the external memory allocation and/or theregion may be transferred from one client to another. Ownership may bean association in the metadata of the external memory allocation and/orthe region with the client, an account on the client, and/or a virtualmachine on the client. A capability to transfer ownership from oneclient to another may facilitate moving the application logic from oneclient to another client more efficiently and/or more rapidly. Forexample, the application logic may include a virtual machine that is tobe migrated from a hypervisor running on a first client to a hypervisorrunning on a second client. When migrating data of the virtual machine,the hypervisors or other component may elect not to migrate data that isstored in the external memory allocation and/or the region. Thehypervisors or other component may instead transfer ownership of and/oraccess to the external memory allocation and/or the region from thefirst client to the second client. For example, the allocation logic 412may update the metadata to transfer the ownership. By updating themetadata to transfer ownership, the data stored in the external memoryallocation and/or the region may be effectively migrated from hypervisorof the first machine to the hypervisor of the second machine withoutcopying the data. Alternatively, or in addition, ownership of and/oraccess to the external memory allocation and/or the region may beassociated with the virtual machine that is being migrated, and theownership and/or access may be transferred implicitly as the virtualmachine is migrated. Alternatively, or in addition, prior to migratingthe virtual machine, the hypervisor and/or the virtual machine may electto discard cached copies of data that are otherwise stored in theexternal memory allocation and/or the region, which may reduce the totalamount of data to be migrated with the virtual machine. Ownership ofand/or access to the external memory allocation and/or the region may betransferred from one client to another by sending, for example, arequest to modify settings for the region to the region access logic ofeach memory appliance which includes the regions for which ownership orand/or access is being transferred.

The hypervisor, the virtual machine, and/or another component may electto allocate additional external memory for use by the virtual machineusing the methods described in this document. For example, thehypervisor or another component may allocate an additional externalmemory allocation and/or an additional region and assign the additionalexternal memory to the virtual machine. Alternatively, or in addition,the virtual machine may allocate an additional external memoryallocation and/or an additional region for use by the virtual machine.Alternatively or in addition, the hypervisor, the virtual machine,and/or another component may resize an existing external memoryallocation and/or region. Allocating additional external memory for useby the virtual machine may be done in place of or in addition toallocating additional local memory for use by the virtual machine. Forexample, if not enough local memory is available to satisfy the demandof an application running within the virtual machine, additionalexternal memory may be allocated for use by the virtual machine in orderto satisfy all or part of the demand. Using external memory may avoid aneed to otherwise migrate the virtual machine to a different client tosatisfy the virtual machine's demand for memory in cases where notenough local memory is available to allocate for use by the virtualmachine.

Configuring the communication interface 230 to treat portions, such aspages, of the region 214 of the memory 210 as not present may includesetting or clearing one or more indicators conveying the presence and/oraccess permissions of corresponding portions of the region 214. In afirst example, the indicators may include a presence bit, conveying thepresence (or non-presence) of a corresponding portion of the region 214in the memory 210. In a second example, the indicators may include aread-access bit, conveying the permission for one or more clients toperform read-based client-side memory access operations upon thecorresponding portion of the region 214. In a third example, theindicators may include a write-access bit, conveying the permission forone or more clients to perform write-based client-side memory accessoperations upon the corresponding portion of the region 214.Alternatively or in addition, the communication interface 430 may beconfigured to treat all of or a portion of the region 214 as anon-demand paging memory region.

FIG. 8A illustrates a flow diagram of example logic of a systemproviding delayed initialization for the region 214. In the exampleillustrated in FIG. 8A, the creation of the region 214 is requested(802), starting the illustrated flow. The region access logic 212 maybegin by allocating (804) all of or a portion of the memory for theregion 214. Alternately or in addition, the region access logic 212 maynot allocate all of or a portion of the memory for the region 214. Theregion access logic 212 may initialize (806) all of or a portion of thememory for the region 214. Alternately, the region access logic 212 maynot initialize all of or a portion of the memory for the region 214. Theregion access logic 212 may configure (808) the communication interface230. For example, the region access logic 212 may indicate to thecommunication interface 230 the portions of the region 214 that areuninitialized are not present, and the portions of the region 214 thatare initialized are present. Upon completion of configuring thecommunication interface 230, the region 214 may be considered created.After the region 214 is created, the communication interface 230 mayprovide client-side memory access to the region 214 even if the region214 has not been allocated or even if initialization of the region 214has not begun or has not completed.

FIG. 8B illustrates a flow diagram of example logic of a systemproviding delayed restore for the region 214. In other words, in thisexample the initialization involves a restore of data from persistentstorage into the region 214, so the delayed initialization includes adelayed restore. In the example illustrated in FIG. 8A, the restore ofthe region 214 is requested (810), starting the illustrated flow. Theregion access logic 212 may begin by allocating (812) all of or aportion of the memory for the region 214. Alternately, the region accesslogic 212 may not allocate all of or a portion of the memory for theregion 214. The region access logic 212 may copy (814) all of or aportion of persisted data for the region 214 into the memory for theregion 214. Alternately or in addition, the region access logic 212 maynot copy all of or a portion of the data for the region 214. The regionaccess logic 212 may configure (816) the communication interface 230.For example, the region access logic 212 may indicate to thecommunication interface 230 the portions of the region 214 that areuninitialized (not restored) are not present, and the portions of theregion 214 that are initialized (restored) are present. After thecommunication interface 230 is configured, the communication interface230 may provide client-side memory access to the region 214 even if theregion 214 has not been allocated, or even if copying the persisted datainto the region 214 has not begun or has not completed.

FIG. 8C illustrates a flow diagram of example logic of a system handlingan I/O fault for delayed initialization and/or delayed restore for theregion 214. An I/O fault may be generated (818), starting theillustrated flow. The I/O fault may be generated (818), for example, bythe communication interface 230 in response to an attempt to access aportion of the region 214 that is not present using client-side memoryaccess and/or to an attempt to access a portion of the region 214 thatis configured with restricted access permissions. If, for example,memory for the portion has not yet been allocated, the region accesslogic 212 may allocate (820) memory for the portion. If, for example,the memory for the portion has not yet been initialized, the regionaccess logic 212 may initialize (822) the portion. If, for example, thepersisted data for the portion has not yet been copied to the memory forthe portion, the region access logic 212 may copy (824) the persisteddata for the portion into the memory for the portion. The region accesslogic 212 may configure (826) the communication interface 230. Forexample, the region access logic 212 may indicate to the communicationinterface 230 that the portion of the region 214 that was accessed isnow present. After the communication interface 230 is configured, thecommunication interface 230 may provide client-side memory access to theregion 214. Subsequent attempts to access the same portion of the region214 may not result in the communication interface 230 generating an I/Ofault unless, for example, the portion of the region 214 is marked asnot present.

FIG. 9A illustrates a flow diagram of example logic of a system for aregistration of on-demand memory for a memory-mapped file. Operationsmay begin, for example, by receiving (902) a request to create orrestore the region 214. The region access logic 212 may map (904) all ofor a portion of the file into a virtual address space. The region accesslogic 212 may register (906) the corresponding portion of the virtualaddress space with the communication interface 230. As a result, thecommunication interface 230 may be configured to treat the registeredportion of the virtual address space as an on-demand paging memoryregion.

The virtual address space may include one or more page tables and/orpage table entries. Alternatively or in addition, the virtual addressspace may include one or more data structures mapping virtual addressesto offsets of the file. Alternatively or in addition, the virtualaddress space may include one or more data structures mapping virtualaddresses to one or more portions of a page cache. The page cache mayinclude one or more portions of memory including data that is cachedfrom and/or for one or more files.

The file may be a regular file in a filesystem, a special file, a blockdevice file, a character device file, a pseudo file, any other type offile, and/or any other interface that can be memory-mapped. The file maybe backed by any medium capable of holding data, such as a solid statememory, a random access memory (RAM), a dynamic random access memory(DRAM), a static random access memory (SRAM), a flash memory, aread-only memory (ROM), an electrically erasable programmable read-onlymemory (EEPROM), a flash memory, a phase change memory, a memristormemory, a solid state storage device, a magnetic disk, tape, othermedia, and/or any one or more byte-addressable and/or block-addressablemedia now known or later discovered. In one example, the file mayinclude an interface to enable memory mapping to a peripheral thatenables access to solid state memory, such as a PCIe-attachedflash-memory peripheral. In another example, the file may include aninterface, such as an interface in a virtual filesystem, which enablesaccess to a corresponding area of memory in a memory appliance. As such,reading or writing data to a specified offset within the file may causethe virtual filesystem to read or write data from the correspondingoffset within the memory of the memory appliance. Similarly, when thefile is memory-mapped, page faults in memory backed by the file maycause the virtual filesystem to read data from the corresponding offsetwithin the memory of the memory appliance, and/or writeback to the filemay cause the virtual filesystem to write data to the correspondingoffset within the memory of the memory appliance. The memory appliancemay be external to the computing system that is executing the kerneldriver and/or the virtual filesystem. Alternatively or in addition, thefile may be the backing store 260 or may be included in the backingstore 260.

In at least one example, the file may include an interface, such as aninterface in a virtual filesystem, that allows access to a correspondingarea of memory in a second memory appliance. As such, writing data tothe file may serve as a way to replicate data from the memory applianceto the second memory appliance. Alternatively, or in addition, writingdata to the file may serve as a way to migrate data from the memoryappliance to the second memory appliance. The second memory appliancemay have differing characteristics and/or configurations, such as higherlatency, lower bandwidth, and/or any other different characteristicsand/or configurations as described above. The second memory appliancemay, in turn, use any of the techniques described in this document toprovide client-side memory access to one or more regions.

FIG. 9B illustrates a flow diagram of example logic of a system handlingan I/O fault of on-demand memory for the memory-mapped file. Operationsmay begin by, for example, the communication interface 230 generating(908) an I/O fault in response to an attempt to access a portion of theregion 214 that is not present using client-side memory access and/or anattempt to access a portion that is configured with restricted accesspermissions. An I/O fault interrupt handler may be invoked (910) with adevice driver, in response to the I/O fault. In some examples, the I/Ofault handler may cause an operating system to trigger one or more pagefaults on a corresponding portion of the virtual address space. Forexample, the I/O fault handler may invoke (912) a get-user-pagesprogrammatic procedure to trigger the page faults. The file's faulthandler may handle (914) the page faults by allocating, initializing,and/or copying data into portions of the memory, similar to as describedfor FIG. 8C. Alternatively or in addition, one or more of theseoperations may be performed by the operating system. For example, theoperating system may allocate the portions of the memory. Uponcompletion of the page fault handling, the device driver may configure(916) the communication interface 230. For example, the device drivermay indicate to the communication interface 230 that the accessedportion(s) of the memory are present. Upon completion of configuring thecommunication interface, the system may resume normal operation.

The device driver, the operating system, and/or the file's fault handlerare shown as separate entities in FIG. 9B for illustrative/claritypurposes only and are not intended to imply that they must be separateentities, nor that they must be separate from the other parts of thesystem. For example, the device driver, the operating system, and/or thefile's fault handler may each be included in the region access logic212. Alternatively or in addition, each may be included in differentlogics and/or may be an independent logic.

The region access logic 212 may pin all of or a portion of the portionof the virtual address space in the memory 210. Alternatively or inaddition, the region access logic 212 may not pin any of the portion ofthe virtual address space in the memory and/or may delay pinning. Forexample, the region access logic 212 may pin portions of the virtualaddress space which the application expects to be available forperforming client-side memory access operations upon with minimumlatency, such as portions containing one or more lookup tables,journals, metadata, and/or any other data. Pinning a portion in memorymay include exercising an interface and/or calling a programmaticprocedure in an operating system, which causes the operating system toavoid invalidating and/or reclaiming a portion of memory specified viathe interface and/or programmatic procedure. Unpinning a portion inmemory may include exercising an interface and/or calling a programmaticprocedure in an operating system which causes the operating system tocancel a previous pin operation. As a result, the operating system mayno longer avoid invalidating and/or reclaiming the portion specified viathe interface and/or function.

Alternatively or in addition, the region access logic 212 may populateand/or pin a portion of the portion of the virtual address space in thememory upon receiving a request from the client logic 312, such as aprefetch request and/or a pin request. Alternatively or in addition, theregion access logic 212 may un-pin the portion of the virtual addressspace upon receiving an unpin request.

FIG. 10A illustrates a flow diagram of example logic of a systemhandling a pre-fetch request. Operations may begin with the client logic312 sending (1002) a pre-fetch request to the region access logic 212.The pre-fetch request may specify one or more portions to populate. Theregion access logic 212 may handle the pre-fetch request by pre-fetching(1004) the requested portions. Pre-fetching the requested portions mayinclude, for example, issuing one or more pre-fetch commands, such asverbs, to the communication interface 230 and/or the device driver.Alternatively, or in addition, pre-fetching the requested portions mayinclude triggering one or more page faults and/or I/O faults for therequested portions. Upon completing handling of the pre-fetch request,the region access logic 212 may send a completion status to the clientlogic 312 and/or the pre-fetch operation may be complete (1006).

FIG. 10B illustrates a flow diagram of example logic of a systemhandling a pin request. Operations may begin with the client logic 312sending (1008) a pin request to the region access logic 212. The pinrequest may specify one or more portions to pin and/or durations forwhich to pin the portions. The region access logic 212 may handle (1010)the pin request by pre-fetching the requested portions, pinning therequested portions in memory, and/or starting a timer for the specifiedduration. Upon completing handling of the pin request, the region accesslogic 212 may send a completion status to the client logic 312 and/orthe pin operation may be complete (1012). Upon expiration of the timer,which may occur before or after the pin operation completes, the regionaccess logic 212 may unpin the corresponding portions.

FIG. 10C illustrates a flow diagram of example logic of a systemhandling an unpin request. Operations may begin with the client logic312 sending (1014) a pin request to the region access logic 212. Theunpin request may specify one or more portions to un-pin. The regionaccess logic 212 may handle (1016) the unpin request by un-pinning thespecified portions. Upon completing handling of the unpin request, theregion access logic 212 may send a completion status to the client logic312 and/or the unpin operation may be complete (1018).

FIG. 10D illustrates a flow diagram of example logic of a systemhandling a reclaim request. Operations may begin with the client logic312 sending (1020) a reclaim request to the region access logic 212. Thereclaim request may specify one or more portions to reclaim. The regionaccess logic 212 may handle (1022) the reclaim request by causing theportions to be invalidated and/or reclaimed, as described elsewhere inthis document. Upon completing handling of the reclaim request, theregion access logic 212 may send a completion status to the client logicand/or the reclaim operation may be complete (1024).

The memory 210 may be of sufficient capacity to hold all of the data ofone or more regions. Alternatively, the memory 210 may not have enoughcapacity to hold all of the data of the regions. The region access logic212 may select portions of the regions to be included in the memory 210and/or in the backing store 260 and/or may configure the communicationsinterface 230 to treat portions as present when contained in the memory210 and/or not present when not contained in the memory 210.

The region access logic 212 may effectively provide access viaclient-side memory access to the data of a medium that is slower thanthe memory 210, and/or that is not in an address space addressable bythe processor. Accordingly, accesses to portions of the data of themedium that are present in the memory 210 may be performed atmemory-like speeds. Another advantage may be that a memory appliance maybe created that provides multiple price/performance/capacity, etc. tierswith, for example, lower cost, lower performance, and higher capacitythan the memory 210, by using the backing store 260, the file, and/orthe second memory appliance as the next-level tiers.

FIG. 11 illustrates a memory architecture diagram of an example systemproviding multiple tiers of memory. The system may provide one or moretiers of memory. A tier may be a collection of memory with a common setof attributes, such as price, capacity, latency, bandwidth, operationsper second, physical locality, network locality, logical locality,and/or any other attributes of the memory and/or of the devicecontaining the memory. The attributes of a tier involving memory of amemory appliance may include any of the characteristics and/orconfigurations of the memory appliance 110.

The attributes of one tier may differ from those of another tier. In oneexample, price and performance may decrease for lower tiers whilecapacity increases. This may enable the system to naturally demote datafrom higher levels to lower levels as other data proves to be used moreoften and/or more recently.

In at least one example, the highest-level tiers may be provided by thehardware of the client 130. For example, level 1 may be provided by theL1 cache of the processor of the client 130, level 2 may be provided bythe L2 cache of the processor of the client 130, level 3 may be providedby the L3 cache of the processor of the client 130, level 4 may beprovided by the memory 310 of the client 130, and/or another level maybe provided by the backing store 360 of the client 130.

In at least one example, one or more tiers may be provided by one ormore memory appliances. For example: level 5 may be provided by one ormore memory appliances with very low latency and/or high bandwidth;level 6 may be provided by one or more memory appliances with higherlatency, lower bandwidth, and/or higher capacity; level 7 may beprovided by the backing store of one or more memory appliances and/or ofthe client.

A logic, such as the client logic 312 and/or the region access logic 212may cause data for one or more portions of the region 214 to be migratedto lower-numbered tiers by causing the data of the portions to befaulted-in at the desired level. In one example, the client logic 312may attempt to read the data, causing the data to be loaded into thememory of the client 312 and/or into one or more levels of processorcache of the client. Alternatively, or in addition, the client logic 312may pre-fetch the data, such as by issuing a pre-fetch request with anoperating system of the client. The pre-fetch request may be a memoryadvisory request, indicating that the client logic will need the data.In another example, the client logic 312 may send a pre-fetch request tothe region access logic 212. Such as described for FIG. 10A, thepre-fetch request may cause the data to be loaded into the memory 210 ofthe memory appliance 110. In another example, the client logic 312 maysend a pin request to the region access logic 212. Such as described forFIG. 10B, the pin request may cause the data to be loaded into thememory 210 of the memory appliance 110.

Alternatively, or in addition, a logic, such as the client logic 312and/or the region access logic 212 may cause the data for one or moreportions of the region 214 to be migrated away from lower-numbered tiersby unpinning the corresponding portions of memory and/or by causing theportions to be invalidated and/or reclaimed at the desired level.Causing the portions to be invalidated and/or reclaimed at the desiredlevel may be as described elsewhere in this document. Alternatively, orin addition, the client logic 312 may send an unpin request to theregion access logic 212. Such as described for FIG. 10C, the unpinrequest may cause the data to be unpinned from the memory of the memoryappliance 110. Alternatively, or in addition, the client logic 312 maysend a reclaim request to the region access logic. Such as described forFIG. 10D, the reclaim request may cause the portions to be invalidatedand/or reclaimed from the memory of the memory appliance 110.

Alternatively, or in addition, the operating system of the client and/orof the memory appliance 110 may cause the data for one or more portionsof the region 214 to be migrated away from lower-numbered tiers bycausing the portions to be invalidated and/or reclaimed.

The memory appliance 110 may observe or otherwise identify the memoryaccess operations received via the communication interface 230. Forexample, the observer logic 218 of the memory appliance 110 may receivea notification from the client logic 312 indicating one or moreattributes of a memory access operation about to be sent or of a memoryaccess operation just received. In another example, the observer logic218 may receive an indication from the communication interface 230indicating one or more attributes of the memory access operationreceived, such as the immediate data which may be received with a writewith immediate data operation. In response to identifying the memoryaccess operations, the memory appliance 110 may, for example, copy thedata of the region 214 to one or more backing stores 260 independentlyof performing the memory access operations on the memory 210.Furthermore, the memory appliance 110 may perform any action related tothe memory access operation such as copying the portion of the memory tothe backing store 260 and/or indicating to an operating system that theportion has been accessed and/or written-to.

The memory appliance 110 may rely upon the operating system to determineportions of the region 214 to invalidate and/or reclaim for otherpurposes, such as to handle page faults for other portions and/or otherregions. Alternatively or in addition, the region access logic 212 mayselect portions to invalidate and/or reclaim and/or may cause theportions to be invalidated and/or reclaimed. In one example, theoperating system may determine that portions of the region 214 are to beinvalidated and/or reclaimed upon handling a request for memory from theregion access logic 212 and/or any other logic of the system. In anotherexample, the region access logic 212 may determine that portions of theregion 214 are to be invalidated and/or reclaimed upon handling a pagefault and/or I/O fault, such as when needing to allocate memory for thefaulting portion.

Causing the portions of the region 214 to be invalidated and/orreclaimed may include unmapping one or more page table entries for theportions, shooting-down one or more entries in one or more translationlookaside buffers for the page table entries, flushing the translationlookaside buffers, configuring the communication interface 230, and/orfreeing the memory associated with the portions. Configuring thecommunication interface 230 may include unmapping one or more page tableentries used by the communication interface 230 for the portions,shooting-down one or more entries in one or more translation lookasidebuffers used by the communication interface 230 for the page tableentries, and/or flushing the translation lookaside buffers used by thecommunication interface 230.

Causing the portions of the region 214 to be invalidated and/orreclaimed may be performed upon multiple portions as in a batchedinvalidation and/or reclaim operation. For example, the region accesslogic 212 may unmap one or more page table entries for multiple portionsthen flush the affected translation lookaside buffers, such as thetranslation lookaside buffers for processors that are using the virtualaddress space containing the page table entries at the time the pagetable entries are reclaimed. Alternatively or in addition, the regionaccess logic 212 may not flush translation lookaside buffers forprocessors that are no longer using the virtual address space. Inanother example, the region access logic 212 may unmap one or more pagetable entries used by the communication interface 230 for the multipleportions and then flush the translation lookaside buffers used by thecommunication interface 230.

FIG. 12A illustrates a flow diagram of example logic of a systemperforming batched portion unmap. The region access logic 212 may beginby selecting (1204) a portion to unmap. The portion may be selectedbased on the state of portion-tracking data structures. For example, theportion may be the next page to unmap in a list of pages ordered by timeof last use.

Upon selecting the portion to unmap, the region access logic may unmap(1206) page table entries for the portion. Unmapping page tables for theportion may include clearing page table entries, shooting-down one ormore entries with one or more translation lookaside buffers (TLB's),flushing one or more translation lookaside buffers (TLB's) forprocessors using the virtual address space, and/or updating datastructures associated with the portion. Alternatively or in addition,unmapping page tables for the portion may not include shooting downentries and/or flushing one or more TLB's at this time. In lieu ofshooting down entries and/or flushing one or more TLB's, the regionaccess logic 212 may update page-tracking data structures and/or datastructures associated with the portion. In one example, the regionaccess logic 212 may update one or more flags included in the datastructures associated with the portion, indicating that one or moreTLB's have not been flushed for the portion. In another example, theregion access logic 212 may update one or more generation countersincluded in the data structures associated with the portion, indicatingthe logical time at which a page table entry was last cleared for theportion and/or for a processor. A generational counter may be a valuethat may be incremented with each event, which may be used to identifythe order in which events have occurred. In another example, updatingportion-tracking data structures may include updating a bitmask ofprocessors needing a TLB flush to indicate that a TLB flush will beneeded for the processors using the virtual address space.

Upon unmapping the page table entries, the region access logic 212 mayconfigure (1208) the communication interface 230. Configuring thecommunication interface 230 may include configuring the communicationinterface 230 and/or updating data structures with the communicationinterface 230 to indicate that the portion is not present. Configuringthe communication interface 230 may include shooting down entries withand/or flushing a TLB or similar mechanism with the communicationinterface 230. Alternatively, the entries may not be shot down and/orthe TLB or similar mechanism may not be flushed at this time.

Upon configuring the communication interface 230, the region accesslogic 212 may update (1210) the portion-tracking data structures. Forexample, the portion may be moved to a list of portions that have beenunmapped but not reclaimed.

Upon updating the portion-tracking data structures, the region accesslogic 212 may check (1212) if more portions should be unmapped. Forexample, the region access logic 212 may check if the portion-trackingdata structures indicate that too many portions and/or pages are in usefor the region 214 and not yet unmapped. If the region access logic 212determines that more portions should be unmapped, the process mayrestart by selecting (1204) the next portion to unmap.

Alternatively, if the region access logic 212 determines that no moreportions should be unmapped, the region access logic 212 may check(1214) if portions should be reclaimed. For example, the region accesslogic 212 may check if the portion-tracking data structures indicatethat too many portions and/or pages are in use for the region. If theregion access logic 212 determines that portions should not bereclaimed, the batched portion unmap may be complete, and the regionaccess logic 212 may resume normal operation. Alternatively, if theregion access logic 212 determines that portions should be reclaimed,the region access logic 212 may trigger (1216) a batched portioninvalidation and/or reclaim process, such as the process illustrated inFIG. 12B, and resume normal operation.

FIG. 12B illustrates a flow diagram of example logic of a systemperforming batched portion invalidation/reclaim. The region access logic212 may begin by flushing (1218) one or more TLB's, if necessary. Forexample, if one or more TLB entries were not shot down and/or one ormore TLB's were not flushed when one or more page table entries wereunmapped, then one or more TLB flushes may be necessary prior toreclaiming the portions associated with the page table entries. Theregion access logic 212 may check the portion-tracking data structuresand/or data structures associated with the portion to determine whetheror not one or more TLB's need to be flushed and/or may flush the TLB's.For example, one or more TLB's may need to be flushed if the bitmask ofprocessors needing a TLB flush indicates that the TLB's need to beflushed. Alternatively or in addition, the region access logic 212 mayflush TLB's without checking whether it is necessary to do so.

Flushing the TLB's may include updating the portion-tracking datastructures and/or data structures associated with the portion toindicate that one or more TLB flushes have been performed and/or thatone or more portions do not need the TLB flushed before they may bereclaimed. In one example, updating portion-tracking data structures mayinclude updating a bitmask of processors needing a TLB flush to indicatethat a TLB flush is no longer needed for the flushed TLB's. In oneexample, updating portion-tracking data structures may include updatingone or more generation counters, indicating the logical time at whichthe TLB was flushed.

After flushing TLB's (if necessary), the region access logic 212 mayconfigure (1220) the communication interface 230, if necessary. Forexample, if entries were not shot down with and/or the TLB or similarmechanism was not flushed with the communication interface 230 whenconfiguring the communication interface 230 and/or updating datastructures to indicate a portion was not present, then the TLB orsimilar mechanism may need to be flushed. The region access logic 212may check the portion-tracking data structures and/or data structuresassociated with the portion to determine whether or not the TLB orsimilar mechanism needs to be flushed and/or may flush the TLB orsimilar mechanism. Alternatively or in addition, the region access logicmay flush TLB or similar mechanism without checking whether it isnecessary to do so.

Flushing the TLB or similar mechanism may include updating theportion-tracking data structures and/or data structures associated withthe portion to indicate that the TLB (or similar mechanism) flush hasbeen performed and/or that one or more portions do not need the TLB orsimilar mechanism flushed before they may be reclaimed.

After configuring the communication interface 230 (if necessary), theregion access logic 212 may select (1222) a portion to reclaim. Theportion may be selected based on the state of portion-tracking datastructures. For example, the portion may be the next portion to reclaimin a list of portions that have been unmapped but not reclaimed.

After selecting a portion to reclaim, the region access logic 212 maycheck (1224) if the portion is mapped to any page table entries. If so,then the region access logic 212 may update (1226) portion-tracking datastructures and/or move on to select (1222) a different portion toreclaim. Updating the portion-tracking data structures may includemoving the portion to the list of portions ordered by time of last use.

If the portion is not mapped to any page table entries, then the regionaccess logic 212 may check (1228) if the portion is under writeback. Theportion may be under writeback if the contents of the portion arecurrently being written to the file and/or the backing store 260. If theportion is under writeback, then the region access logic 212 may move onto select (1222) a different portion to reclaim.

Alternatively, if the portion is not under writeback, then the regionaccess logic 212 may check (1230) if the portion is dirty. The portionmay be dirty if the portion contains data which has been written to, butwhich has not yet been written back to the file and/or the backing store260. If the portion is dirty, the region access logic 212 may startwriteback (1232) of the portion and may move on to select (1222) adifferent portion to reclaim.

If the portion is not dirty, then the region access logic 212 mayreclaim (1234) the portion. Reclaiming the portion may includetriggering operations similar to as described for FIG. 12C.Alternatively, or in addition, reclaiming the portion may includefreeing the memory associated with the portion.

After reclaiming the portion, the region access logic 212 may check(1236) whether more portions should be reclaimed from those that havehad the TLB flushed. For example, the region access logic 212 may checkif the portion-tracking data structures indicate that too many portionsand/or pages are in use for the region 214 and/or may check if a list ofportions that have had the TLB flushed is not empty. If the regionaccess logic 212 determines that more portions should be reclaimed fromthose that have had the TLB flushed, the region access logic 212 maymove on to select (1222) the next portion to reclaim.

If there are no portions to reclaim that have had the TLB flushed, thenthe region access logic 212 may check (1238) whether more portionsshould be reclaimed. For example, the region access logic 212 may checkif the portion-tracking data structures indicate that too many portionsand/or pages are in use for the region and/or may check if the list ofportions that have been unmapped but not reclaimed is empty. If theregion access logic 212 determines that more portions should bereclaimed, the process may restart by flushing (1218) TLB's, ifnecessary. If the region access logic 212 determines that no moreportions should be reclaimed, the region access logic 212 may resumenormal operation.

FIG. 12C illustrates a flow diagram of an example logic of a systemreacting to a pending reclaim operation. The region access logic 212 mayreact to the pending reclaim operation by flushing (1240) one or moreTLB's if necessary. Upon flushing one or more TLB's (if necessary), theregion access logic 212 may configure (1242) the communication interface230, if necessary. After configuring the communication interface (ifnecessary), the region access logic 212 may update (1244) theportion-tracking data structures. For example, the region access logic212 may remove the portion from the portion-tracking data structuresand/or may update information reflecting the number of portions and/orpages that are in use for the region. Upon updating the portion-trackingdata structures, reacting to the pending reclaim operation is complete,and the region access logic 212 may resume normal operation.

Alternatively or in addition, the region access logic 212 may use thetechniques described in this document to provide point-in-time snapshotsof the region 214 that are accessible via client-side memory access. Forexample, the region access logic 212 may configure the communicationinterface 230 to direct client-side memory access operations to operateon the same portions of the memory and/or of the file for both a firstregion and a second region, where the second region is a virtual copy orsnapshot of the first region. The region access logic 212 may initiallyconfigure the communication interface 230 to treat one or more portionsof both regions as not writable, such that attempts to write to any ofthe portions may cause the communication interface 230 to trigger a pagefault with the region access logic 212. For example, the region accesslogic 212 may configure the communication interface 230 to treat allportions of both regions as not writable.

Alternatively, or in addition, the region access logic 212 may initiallyconfigure the communication interface 230 to treat one or more portionsof both regions as not present, such that attempts to read or write toany of the portions may cause the communication interface 230 to triggera page fault with the region access logic. For example, the regionaccess logic 212 may configure the communication interface 239 to treatall portions of both regions as not present.

Upon a page fault being triggered with the region access logic, theregion access logic 212 may perform a copy operation and resume theclient-side memory access operation. Alternatively, or in addition, theregion access logic 212 may cause the client-side memory accessoperation to fail.

FIG. 13 illustrates a flow diagram of example logic of a systemproviding point-in-time snapshots with copy-on-write in a page-faulthandler. The process may start when a page fault in the operating systemand/or an I/O fault in the communication interface 230 occurs (1302)upon a faulted portion of the region 214. The region access logic 212may start by checking (1304) whether the page fault was for a writeattempt or not.

If the page fault was not for a write attempt, the region access logic212 may check (1306) if there is a page marked up-to-date in file datafor the file offset of the faulting file. If so, the page may beselected and the remaining operations described in this paragraph may beskipped. If not, then the region access logic 212 may look up (1308) adata origin file in the data structures. Upon looking up the data originfile in the data structures, the region access logic 212 may check(1310) if there is a page in the file data for the file offset of theorigin file and perform a copy operation. If there is a page in the filedata, the copy operation may include copying (1312) the data from thefile data of the origin file to the file data of the faulting file. Ifthere is not a page in the file data, then the copy operation mayinclude copying (1314) the data from the faulting file (if present) orthe origin file to the file data of the faulting file. Upon completionof the copy operation, the region access logic may mark (1316) the pagein the file data for the faulting file as up-to-date.

With a page marked up-to-date in the file data for the file offset ofthe faulting file, the region access logic 212 may optionally check(1318) whether the page is shared with another file, such as if thefaulting file were an origin file for a second faulting file. If so, theregion access logic 212 may optionally install (1322), with read-onlypermission, the page in the virtual address corresponding with theregion and may complete (1320) the page fault operation. If not, theregion access logic 212 may optionally install (1324), with read-writepermission, the page in the virtual address corresponding with theregion 214 and may complete (1320) the page fault operation.

If the page fault was for a write attempt, then the region access logicmay check (1326) whether the page is shared with another file. If so,the region access logic 212 may perform a copy operation. The copyoperation may include copying (1328) data from the original page to anew page in the file data. Upon completion of the copy operation, theregion access logic 212 may mark (1330) the new page in the file data asup-to-date and may optionally install (1324), with read-writepermission, the page in the virtual address corresponding with theregion 214 and may complete (1320) the page fault operation. On theother hand, if the page is not shared with another file, then the regionaccess logic 212 may mark (1332) page-table entry as writable, andcomplete (1320) the page fault operation.

Upon completing the page fault operation, the region access logic 212may configure (1334) the communication interface 230 and resume normaloperation.

The data structures may be similar to the data structures, the kerneldata structures, and/or the kernel driver data structures as describedin U.S. Provisional Patent Application 62/139,310 entitled “FORK-SAFEMEMORY ALLOCATION FROM MEMORY-MAPPED FILES WITH ANONYMOUS MEMORYBEHAVIOR” and filed Mar. 27, 2015, which is hereby incorporated byreference. For example, the data structures may include one or morelists, trees, hash tables, and/or other data structures to associateorigin files with one or more files which may share pages with theorigin files and/or which enable the efficient lookup of an origin filefor a given faulting file and/or page. The data structures may beincluded in the region metadata.

The file data may include one or more portions of the contents of afile. The one or more portions may be uniform in size. For example, theone or more portions may each be the size of a memory page. The filedata may include cached pages that have been read via the memory-mappedinterface and/or that have been written to, but that may not have beenwritten back to the file. In at least one example implementation, thefile data may be included in a page cache, a buffer cache, and/or anyother type of cache. The file may be included in the memory of thememory appliance. For example, the file may be included in the region.Alternatively or in addition, the file may be the region.

FIG. 14 illustrates a flow diagram of example logic of a systemproviding point-in-time snapshots with copy-on-access in a page-faulthandler. The process may start when a page fault and/or I/O fault occurs(1402) upon a faulted portion of the region. The region access logic 212may start by checking (1404) if there is a page marked up-to-date in thefile data for the file offset of the faulting file. If so, the page maybe selected and the remaining steps in this paragraph may be skipped. Ifnot, the region access logic 212 may look up (1406) a data origin filein the data structures. After looking up the data origin file in thedata structures, the region access logic 212 may check (1408) if thereis a page in the file data for the file offset of the origin file andperform a copy operation. If there is a page in the file data, the copyoperation may include copying (1410) the data from the file data of theorigin file to the file data of the faulting file. If there is not apage in the file data, the copy operation may include copying (1412) thedata from the faulting file (if present) or the origin file to the filedata of the faulting file. Upon completion of the copy operation, theregion access logic 212 may mark (1414) the page in the file data forthe faulting file as up-to-date.

Upon completing the above steps, the region access logic 212 mayoptionally install (1416), with read-write permission, the page in thevirtual address corresponding with the region 214 and may complete(1418) the page fault operation. Upon completing the page faultoperation, the region access logic 212 may configure (1420) thecommunication interface 230, and resume normal operation.

The copy operation may include copying data from a first portion of afirst region to a second portion of a second region. Alternatively, orin addition, the copy operation may include copying data from one orboth portions to one or more files and/or to the backing store 260.Alternatively, or in addition, the copy operation may include copyingdata from the files and/or the backing store 260 to one or both portionsand/or copying data between multiple files and/or multiple portions ofthe backing store 260.

For example, if the portion being written to via client-side memoryaccess is not contained in the memory for either region, the data forthe portion may be copied from a first portion of a first file(corresponding to the first portion of the first region) to the firstportion of the first region. Alternatively or in addition, the data forthe portion may be copied from the first portion of the first file to asecond portion of a second file (corresponding to the second portion ofthe second region). Alternatively or in addition, metadata associatedwith the files may be updated such that the first portion of the firstfile becomes associated with the second file, replacing the secondportion of the second file. Alternatively or in addition, the first fileand the second file may be copy-on-write snapshots of one-another, suchas in a copy-on-write-capable filesystem, partitioning system, storagesystem, and/or any other system capable of maintaining a copy-on-writerelationship between files.

Resuming the client-side memory access operation may include allowing aclient-side memory access operation to proceed to either the firstportion or the second portion (or both portions). Allowing a client-sidememory access operation to proceed may include configuring thecommunication interface 230 to treat the first portion and/or the secondportion as writable (and/or present) and/or to direct client-side memoryaccesses to one or both regions to operate upon different portions ofthe memory, such as the portion of the memory written to by the copyoperation.

Alternatively or in addition, the region access logic 212 may performadditional copy operations, such as by predicting future page faultsbased on an observed pattern of prior page faults. For example, theregion access logic 212 may perform copy operations upon the portions offiles corresponding to the predicted future page faults. The regionaccess logic 212 may use any mechanism or combination of mechanisms forpredicting the future page faults, such as fixed synchronousprefetching, adaptive synchronous prefetching, fixed asynchronousprefetching, adaptive asynchronous prefetching, perfect prefetching,and/or any other mechanism known now or later discovered.

Alternatively or in addition, the region access logic 212 may providepoint-in-time snapshots by forking a parent process that had previouslyregistered a portion of its virtual address space as an on-demand memoryregion. The region access logic 212 may take additional steps to ensurethat the registered on-demand memory region for the child process may bereferenced differently than for the parent process, such as bytemporarily unregistering the parent process's on-demand memory,re-registering the parent process's on-demand memory, and/or registeringa portion of the child process's virtual address space with on-demandmemory.

The portion of the virtual address space may be mapped to anonymousmemory. Alternatively, or in addition, the portion of the virtualaddress space may be mapped to one or more files, such as described inU.S. Provisional Patent Application 62/139,310 entitled “FORK-SAFEMEMORY ALLOCATION FROM MEMORY-MAPPED FILES WITH ANONYMOUS MEMORYBEHAVIOR” and filed Mar. 27, 2015, which is incorporated by reference.

Forking the parent process may cause a child process to be created whichinitially has an identical virtual address space to the parent process.Changes to the contents of memory mapped into the child process'svirtual address may be applied in the child process's virtual addressspace but may not be applied in the parent process's virtual addressspace. Changes to the contents of memory mapped into the parentprocess's virtual address may be applied in the parent process's virtualaddress space but may not be applied in the child process's virtualaddress space. Similarly, changes made via client-side memory access tothe contents of memory mapped into either process's virtual addressspace may only be applied to the corresponding process's virtual addressspace.

In one aspect, the memory appliance may be provided comprising aprocessor, a communication interface, a memory, and a region accessunit. The memory may be configured in an address space addressable bythe processor. The region access unit may be configured to allocate aregion of the memory for use as an external primary memory of a clienton a network. The external primary memory of the client may be primarymemory of the client that is external to the client and is accessible tothe client over the network via the communication interface of thememory appliance. The communication interface may be configured toprovide the client access to the region of the memory via client-sidememory access before initialization of all of the region, where theprocessor of the memory appliance may be bypassed if a client-sidememory access request is for an initialized portion of the region of thememory but if the client-side memory access request is for anuninitialized portion of the region, then the processor is configured toinitialize the uninitialized portion in response to the client-sidememory access request.

Initialization of the uninitialized portion may include a setting of theuninitialized portion to all zeros or all ones. Alternatively or inaddition, initialization of the uninitialized portion may include acopying of data from a backing store to the uninitialized portion.Initialization of the uninitialized portion may include a copying ofdata from a second memory appliance to the uninitialized portion.Initialization of the region may include a restore of the region of thememory after a reboot of the memory appliance, where a portion of theregion of the memory that has never been written to after allocation isset to all zeros or all ones instead of being restored.

The region access unit may be configured to configure the communicationinterface to treat portions of the region of the memory as uninitializedbased on a setting and/or a clearing of one or more indicatorsindicative of presence and/or access permission of the portions of theregion. In some examples, the region access unit is configured toallocate the region of the memory for the client after client-sidememory access to the region is provided.

In a second aspect, method to create a virtual copy of memory may beprovided. Client-side memory access may be provided to a first memoryregion of a memory of a computing device, where the memory is in anaddress space addressable by a processor of the computing device. Theclient-side memory access may be provided via a communication interfaceof the computing device by-passing the processor. Client-side memoryaccess may be provided to a second memory region of the memory of thecomputing device via the communication interface, where the secondmemory region is a virtual copy of the first memory region. Client-sidememory access may be provided to the second memory region without havingcopied all of the first memory region to the second memory region. Arequest to read a portion of the second memory region may be receivedvia the communication interface. Data from a corresponding portion ofthe first memory region may be returned in response to the request toread the portion of the second memory region if the portion of thesecond memory region and the corresponding portion of the first memoryregion have not been written to and/or accessed after client-side memoryaccess was provided to the second memory region and returning data fromthe second memory region if the portion of the second memory region orthe corresponding portion of the first memory region have been writtento and/or accessed after client-side memory access was provided to thesecond memory region. Providing client-side memory access to the secondmemory region may include, for example, registering the second memoryregion with the communication interface.

A portion of the first memory region and a corresponding portion thesecond memory region may be marked as not present if the portion of thefirst memory region and the corresponding portion of the second memoryregion have not been written to and/or accessed after client-side memoryaccess was provided to the second memory region, but may be marked aspresent if the portion of the first memory region or the correspondingportion of the second memory region has been written to and/or accessedafter client-side memory access was provided to the second memoryregion.

In one interesting aspect, the client-side memory access may be providedto the second memory region in response to a request received via thecommunication interface from a client of the computing device. Therequest may be a custom command of a memory access protocol thatrequests a virtual copy of the first memory region to be made.Alternatively or in addition, the client-side memory access may beprovided to the second memory region in response to input received in agraphical user interface, a command line interface, a textual interface,or any other user interface, where the input indicates that the virtualcopy is to be made.

The first and second memory regions may be primary external memory to aclient of the computing device. Alternatively or in addition, theclient-side memory access may be provided to the second memory region inresponse to a request received by a region access unit of the computingdevice.

In some examples, data may be copied to the portion of the second memoryregion from the corresponding portion of the first memory region inresponse to access of the portion of the second memory region or thecorresponding portion of the first memory region. Alternatively or inaddition, the data may be copied to the portion of the second memoryregion from the corresponding portion of the first memory region inresponse to a write to the portion of the second memory region or to thecorresponding portion of the first memory region.

In a third aspect, a system may be provided that comprises acommunication interface configured to communicate over a network, aprocessor, and a memory configured in an address space addressable bythe processor. The processor may be configured to memory map at least aportion of a file to a memory region included in the memory, wherein avirtual address addressable by the processer is generated, and the atleast a portion of file is accessible through the memory region at thevirtual address. The virtual address may be registered with thecommunication interface, where registration of the virtual addressprovides client-side memory access to the memory region. The client-sidememory access may provide a client of the system access to the memoryregion over a network, the memory region accessible independently of theprocessor via memory access operations received from the client by thecommunication interface, wherein the memory access operations conform toa memory access protocol, such as RDMA.

In some examples, the memory region may be primary external memory tothe client. Alternatively or in addition, the file may be stored on amemory appliance external to the system.

The processor may be configured to change data in a portion of thememory region from a first memory tier to a second memory tier.Alternatively or in a addition, the processor may be configured to trackand mark as dirty any portion of the memory region that is written tovia an observable write, and write dirty portions of the memory regionto the file but portions of the memory region that are not dirty are notwritten to the file.

The processor may be configured to perform a batch portion invalidationand/or reclaim of portions of the memory region and indicate to thecommunication interface that the portions of the memory region arereclaimed and/or invalidated. Alternatively or in addition, the memoryregion may not be large enough to store all of the at least a portion ofthe file at once.

The client 130, the memory appliance 110, and the management server 120may be configured in any number of ways. In one example, the memoryappliance 110 may be included in a computer. For example, the processormay be the CPU of the computer, the memory may be the memory of thecomputer, and the computer may include the communication interface 330.Alternatively or in addition, the memory appliance 110 may be aperipheral of a computer, including but not limited to a PCI device, aPCI-X device, a PCIe device, an HTX (HyperTransport eXpansion) device,or any other type of peripheral, internally or externally connected to acomputer.

In a second example, the memory appliance 110 may be added to a computeror another type of computing device that accesses data in the memoryappliance 110. For example, the memory appliance 110 may be a deviceinstalled in a computer, where the client 130 is a process executed by aCPU of the computer. The memory in the memory appliance 110 may bedifferent than the memory accessed by the CPU of the computer. Theprocessor in the memory appliance 110 may be different than the CPU ofthe computer.

In a third example, the memory appliance 110, the client 130, and/or themanagement server 120, may be implemented using a Non-Uniform MemoryArchitecture (NUMA). In NUMA, the processor may comprise multipleprocessor cores connected together via a switched fabric ofpoint-to-point links. The memory controller may include multiple memorycontrollers. Each one of the memory controllers may be electricallycoupled to a corresponding one or more of the processor cores.Alternatively, multiple memory controllers may be electrically coupledto each of the processor cores. Each one of the multiple memorycontrollers may service a different portion of the memory than the othermemory controllers.

In a fourth example, the processor of the memory appliance 110, theclient 130, and/or the management server 120 may include multipleprocessors that are electrically coupled to the interconnect, such aswith a bus. Other components of the memory appliance 110, the client130, and/or the management server 1202, such as multiple memoriesincluded in the memory, the communication interface, the memorycontroller, and the storage controller may also be electrically coupledto the interconnect.

In a fifth example, the external memory system may include multiplememory appliances, multiple regions, multiple region metadatas, multiplemanagement servers, multiple external memory allocation metadatas,multiple allocation logics, multiple client logics, and/or multipleapplication logics.

In a sixth example, the client 130 may provide additional services toother systems and/or devices. For example, the client 130 may include aNetwork Attached Storage (NAS) appliance. Alternatively or in addition,the client 130 may include a Redundant Array of Independent Disks (RAID)head. Alternatively or in addition, the client 130 may providefile-level access to data stored in the memory appliance 110.Alternatively, or in addition, the client 130 may include a database,such as an in-memory database.

In a seventh example, multiple clients may utilize one or more memoryappliances as shared memory. For example, the clients may include orinteroperate with an application logic that relies on massiveparallelization and/or sharing of large data sets. Examples ofapplication logic that may use massive parallelization include logicthat performs protein folding, genetic algorithms, seismic analysis, orany other computationally intensive algorithm and/or iterativecalculations where each result is based on a prior result. Theapplication logic 314 may store application data, application state,and/or checkpoint data in the regions of the one or more memoryappliances and/or in an external memory allocation. The additionalcapabilities of the one or more memory appliances, such as low latencyaccess and persistence to the backing store, may be exploited by theclients in order to protect against application crashes, a loss of powerto the clients, or any other erroneous or unexpected event on any ofclients. The clients may access the one or more memory appliances in away that provides for atomic access. For example, the client-side memoryaccess operations requested by the clients may include atomicoperations, including but not limited to a fetch and add operation, acompare and swap operation, or any other atomic operation now known orlater discovered. An atomic operation may be a combination of operationsthat execute as a group or that do not execute at all. The result ofperforming the combination of operations may be as if no operationsother than the combination of operations executed between the first andlast operations of the combination of operations. Thus, the clients maysafely access the one or more memory appliances without causing datacorruption.

The application logic 314, the client logic 312, the allocation logic412, the observer logic 218, and/or the region access logic 212 may beco-located, separated, or combined. The actions performed by combinedlogic may perform the same or similar feature as the aggregate of thefeatures performed by the logics that are combined. In a first example,all five logics may be co-located in a single device. In a secondexample, the region access logic 212 and the observer logic 218 may becombined into a single logic. In a third example, the client logic 312and the observer logic 218 may be combined into a single logic. In afourth example, the client logic 312 and the region access logic 212 maybe combined. In a fifth example, the observer logic 218 may be in adevice different from the memory appliance 110, such as the managementserver 120 and/or a metadata server. A metadata server may be one ormore hardware and/or software entities that may participate in theprocessing of operations, but may not directly handle the data stored inthe memory appliance 110. The metadata server may track statistics,coordinate persistence, coordinate data duplication, and/or perform anyother activity related to the memory access operations. In a sixthexample, the region access logic 212 and the allocation logic 412 may becombined into a single logic. In a seventh example, the client logic 312and the allocation logic 412 may be combined into a single logic. In aneight example, the client logic 312 and the application logic 314 may becombined into a single logic. Other combinations of the variouscomponents are possible, just a few of which are described here.

The application logic 314, the client logic 312, the allocation logic412, the observer logic 218, and/or the region access logic 212 mayinclude computer code. The computer code may include instructionsexecutable with the processor. The computer code may be written in anycomputer language now known or later discovered, such as C, C++, C#,Java, or any combination thereof. In one example, the computer code maybe firmware. Alternatively or in addition, all or a portion of theapplication logic 314, the client logic 312, the allocation logic 412,the observer logic 218, the region access logic 212 and/or the processormay be implemented as a circuit. For example, the circuit may include anFPGA (Field Programmable Gate Array) configured to perform the featuresof the application logic 314, the client logic 312, the allocation logic412, the observer logic 218, and/or the region access logic 212.Alternatively, or in addition, the circuit may include an ASIC(Application Specific Integrated Circuit) configured to perform thefeatures of the application logic 314, the client logic 312, theallocation logic 412, the observer logic 218, and/or the region accesslogic 212. The circuit may be embedded in a chipset, a processor, and/orany other hardware device.

Alternatively, or in addition, a portion of the application logic 312,the client logic 312, the allocation logic 412, the observer logic 218,and/or the region access logic 212 and the processor may be implementedas part of the one or more communication interfaces or other hardwarecomponent. For example, the one or more communication interfaces orother hardware component may modify a portion of the memory when a writeoperation is performed. The observer logic 218 may periodically checkthe portion of memory and may take further action based on the contentsof the portion and the region associated with the portion. The furtheraction may include determining statistics related to the operations thatare being and/or were performed, identifying portions that are beingand/or have been written to and/or read from, persisting the contents ofthe portions to the backing store 260, duplicating the contents of theportions to a different region, a different memory appliance, anexternal server, and/or a backup device, and/or taking any other actionrelated to the operations.

The system may be implemented in many different ways. Each module orunit, such as the client logic unit, the region access unit, theallocation logic unit, the configuration unit, may be hardware or acombination of hardware and software. For example, each module mayinclude an application specific integrated circuit (ASIC), a FieldProgrammable Gate Array (FPGA), a circuit, a digital logic circuit, ananalog circuit, a combination of discrete circuits, gates, or any othertype of hardware or combination thereof. Alternatively or in addition,each module may include memory hardware, such as a portion of the memory210, for example, that comprises instructions executable with theprocessor 240 or other processor to implement one or more of thefeatures of the module. When any one of the module includes the portionof the memory that comprises instructions executable with the processor,the module may or may not include the processor. In some examples, eachmodule may just be the portion of the memory 210 or other physicalmemory that comprises instructions executable with the processor 240 orother processor to implement the features of the corresponding modulewithout the module including any other hardware. Because each moduleincludes at least some hardware even when the included hardwarecomprises software, each module may be interchangeably referred to as ahardware module.

A non-transitory computer-readable storage medium may be provided thatincludes computer executable instructions. The storage medium mayinclude instructions, which when executed by a processor, receive afirst request for an external primary memory allocation. The firstrequest may be received from an application logic unit of a device,where the first request for the external primary memory allocation is arequest for memory that is external to the device but that is primarymemory to the device. The storage medium may include instructions thatare executable by the processor to determine an allocation strategy forthe external primary memory allocation in response to receipt of thefirst request, where the allocation strategy includes identification ofa memory appliance on which to allocate a region of memory. The storagemedium may include instructions that are executable by the processor tosend, over a network via a communication interface, a second request forallocation of the region of memory on the identified memory appliance.

Determining the allocation strategy may include selecting the memoryappliance from a plurality of memory appliances on which to allocate theregion of memory. Alternatively or in addition, determining theallocation strategy may include determining a number of regions toallocate for the external primary memory allocation.

In some examples, determining the allocation strategy may includeselecting a first memory appliance and a second memory appliance from aplurality of memory appliances, and allocating a first region on thefirst memory appliance and a second region on the second memoryappliance. Alternatively or in addition, determining the allocationstrategy may include provisioning a predetermined amount of externalprimary memory for the client from which memory is allocated to theclient in fulfillment of allocation requests received after receipt ofthe first request for the external primary memory allocation.Determining the allocation strategy may include determining adistribution across a plurality of memory appliances of memory toallocate for the external primary memory allocation based on a networklocation of the device relative to the memory appliances. Alternativelyor in addition, determining the allocation strategy may includedetermining a distribution across memory appliances of memory toallocate for the external primary memory allocation based on a networkbandwidth between the device and the memory appliances. Alternatively orin addition, determining the allocation strategy may include determiningan amount of memory to allocate for the external primary memoryallocation based on a profile associated with the client. In someexamples, the storage medium may include instructions that areexecutable by the processor to receive a request to create, destroy, ormodify the external primary memory allocation.

An apparatus may be provided that includes a client logic unit that maycause, in response to a memory allocation request, allocation ofexternal memory that is accessible by the apparatus over aninterconnect, where the external memory may be memory that is externalto the apparatus. The client logic may access the external memory withclient-side memory access over the interconnect. The external memory maybe reserved for the apparatus until freed.

The apparatus may include a local memory. The client logic unit maycache, in the local memory, portions of data stored in the externalmemory, where the data is accessed in memory access operations performedon the external memory. The client-side memory access may includeexecution of a memory access operation that conforms to the RemoteDirect Memory Access (RDMA) protocol.

The apparatus may include an allocation logic unit that receives arequest from the client logic unit to allocate the external memory,wherein the allocation logic unit may select a memory appliance on whichto allocate a region of the external memory, and the client logic unitmay access the region of the external memory over the interconnect withclient-side memory access.

The memory appliance may be selected for allocation of the externalmemory from multiple memory appliances. The selection may be based onperformance criteria of the memory appliances.

The external memory may be accessible by an application logic unitthrough a data interface included in the apparatus. The data interfacemay be a memory allocation interface, a memory swapping interface, amemory caching interface, a block-level interface, a memory-mappedinterface, a graphics processor unit (GPU) accessible interface, acharacter-level interface, and/or a hardware accessible interface. Insome examples, a peripheral device of the apparatus may be providedaccess to the external memory via the data interface.

A memory appliance may be provided that includes a communicationinterface, a memory, and a region access unit. The region access unitmay receive, over a network via the communication interface, a requestto allocate a portion of the memory for use as an external primarymemory of a client on the network. The external primary memory of theclient may be primary memory of the client that is external to theclient. The region access unit may allocate the portion of the memoryfor the client. The communication interface may provide the clientaccess to the allocated portion of the memory via client-side memoryaccess, where a central processing unit of at least one of the client orthe memory appliance is bypassed in the client-side memory access.

A system may be provided that includes a communication interface and anallocation logic unit. The communication interface may receive a requestto allocate external primary memory for a client. The allocation logicunit may determine a number of regions to allocate across multiplememory appliances on a network as part of the external primary memory.The allocation logic unit may send requests for allocation of theregions to the memory appliances over the network.

The system may include memory that includes external memory allocationmetadata descriptive of external memory allocations. The external memoryallocations may include the allocation of the regions distributed acrossthe memory appliances on the network for the external primary memory.

The external memory allocation metadata may be replicated to amanagement server on the network. The external memory allocationmetadata may be recovered from the management server if the systemfails.

The allocation logic unit may determine, in response to a request toresize the external primary memory allocation, a second number ofregions in which to divide the external primary memory. The allocationlogic unit may further determine a distribution of the second number ofregions across the memory appliances. The distribution of the regions ofthe external primary memory may be based on status information receivedfrom the memory appliances. The allocation logic unit may detect asecond memory appliance on the network that was not previously detected.In response, the allocation logic unit may determine an availability ofthe second memory appliance for redistribution of at least one of theregions for the external primary memory.

An apparatus may be provided that includes a configuration unit thatcreates an indication of an allocation strategy. The indication of theallocation strategy may indicate, to an allocation logic unit, theallocation strategy for allocation of external memory across memoryappliances. The allocation logic unit may determine the allocationstrategy in response to requests for external memory.

The indication of the allocation strategy may indicate one or more stepsand/or rules that the allocation logic unit follows in a determinationof how to allocate the external memory. Alternatively or in addition,the indication of the allocation strategy may include a profile of amemory appliance, a client, and/or a user account. Alternatively or inaddition, the indication of the allocation strategy may include apriority setting associated with a user account. Alternatively or inaddition, the indication of the allocation strategy may include atime-of-day limit for a user account.

Alternatively or in addition, the indication of the allocation strategymay include a duration-of-use limit for a user account. Alternatively orin addition, the indication of the allocation strategy may include amaximum external memory usage limit. Alternatively or in addition, theindication of the allocation strategy may include a network bandwidthsetting associated with a client and/or a user account that indicatesthe allocation strategy is to select the memory appliances having acorresponding network bandwidth. Alternatively or in addition, theindication of the allocation strategy may include a network localitysetting associated with a client and/or a user account that indicatesthe allocation strategy is to select any of the memory appliances thatare within a threshold distance of a client device that requested theexternal memory.

In an example, a non-transitory computer storage medium may includecomputer executable instructions, which when executed by one or moreprocessors, may cause one or more of the following steps to be performedfor dynamic allocation of external primary memory.

A communication interface may receive a first request for an externalprimary memory allocation. The first request may be received over anetwork from a client logic unit. The first request may be for primarymemory that is external to a device on the network that includes theclient logic unit. The one or more processors may determine theallocation strategy for the external primary memory allocation inresponse to receipt of the first request. The allocation strategy mayinclude identification of a memory appliance on which to allocate amemory region. Further, the communication interface may send a secondrequest for allocation of the memory region on the identified memoryappliance. Determining the allocation strategy may include selecting thememory appliance from a plurality of memory appliances on which toallocate the memory region. Determining the allocation strategy mayfurther include determining a number of memory regions to allocate forthe external primary memory allocation. Further yet, determining theallocation strategy may include selecting a first memory appliance and asecond memory appliance from a plurality of memory appliances forallocation of a first memory region on the first memory appliance, andallocation of a second memory region on the second memory appliance.

The dynamic allocation of external primary memory may include aprovisioning of a predetermined amount and/or a maximum amount of memoryto allocate for the client. Alternatively, or in addition, determinationof an amount of memory to allocate for the external primary memoryallocation may be based on a parameter of the first request. In anothercase, the dynamic allocation of external primary memory may involvedetermination of an amount of memory to allocate for the externalprimary memory allocation based on a profile associated with the client.The first request may include a request to create, resize, or modify theexternal primary memory allocation.

In another example, an apparatus may include a local primary memory, oneor more processors to execute an application-task, a client logic unit,and an application logic unit. The client logic unit may cause, inresponse to a memory allocation request by the application-task, arequest for external primary memory to be sent over a network. Therequest may be for external primary memory, which is external to theapparatus. The application logic unit may cache, in the local primarymemory, portions of data stored in the external primary memory that isaccessed in memory access operations associated with the externalprimary memory. The apparatus may further include an allocation logicunit. The allocation logic unit may receive the memory allocationrequest from the application-task. The allocation logic unit may select,in response to the memory allocation request, a memory appliance onwhich to allocate a memory region of the external primary memory. Theallocation logic unit, further, may send, in response to the memoryallocation request, the request for external primary memory over thenetwork to the memory appliance. The memory appliance may be selectedfor allocation of the external primary memory from among a plurality ofmemory appliances. The selection may be based on performance criteria ofthe memory appliances. The application logic unit may be furtherconfigured to access the external primary memory by requests transmittedto a data interface included in the apparatus. The data interface mayprovide access to the external primary memory at a block level and/or acharacter level. Further, a peripheral device of the apparatus mayaccess the external primary memory via the data interface. In theapparatus, region metadata may be associated with the memory regionsallocated as part of the external primary memory. The region metadatamay represent a relationship between the memory regions.

In an example, a memory appliance may include a communication interface,a primary memory, and a region access unit. The region access unit mayreceive, over a network via the communication interface, a request toallocate a portion of the primary memory for use as an external primarymemory of a client on the network. The external primary memory of theclient may be external to the client. The region access unit may furtherallocate the portion of the primary memory. The communication interfacemay enable the client to access the allocated portion of the primarymemory via client-side memory access. A client-side memory access mayenable the allocated portion of the primary memory to be accesseddirectly by the client bypassing a processor of the memory appliance.

The memory appliance may also include a metadata unit. The metadata unitmay initialize the allocated portion of the primary memory in accordancewith parameters provided in the request to allocate the portion of theprimary memory. The parameters may include access parameters.Alternatively, or in addition, the parameters may include an indicationof whether or not the allocated portion of the primary memory is to bepersisted to a backing store of the memory appliance.

A system may include a communication interface and an allocation logicunit. The communication interface may receive a request to allocate anexternal primary memory for a client. The allocation logic unit maydetermine a number of memory regions to allocate distributed across aplurality of memory appliances on a network as part of the externalprimary memory. The allocation logic unit may further send requests forallocation of the respective memory regions. The allocation logic unitmay also determine, in response to a request to resize the externalprimary memory allocation, a new number of memory regions to divide theexternal primary memory. Further, the allocation logic unit maydetermine redistribution of the new number of memory regions of theexternal primary memory allocation across the memory appliances.

The system may further include an allocation metadata unit. Theallocation metadata unit may associate the allocated memory regions fromthe memory appliances with the external primary memory. A distributionof the memory regions of the external primary memory may be based onstatus information received from the memory appliances. The allocationlogic unit of the system may further detect a new memory appliancecommunicably connected to the allocation logic unit, and in response,determine availability of the new memory appliance for allocation of thememory regions for the external primary memory.

All of the discussion, regardless of the particular implementationdescribed, is exemplary in nature, rather than limiting. For example,although selected aspects, features, or components of theimplementations are depicted as being stored in memories, all or part ofsystems and methods consistent with the innovations may be stored on,distributed across, or read from other computer-readable storage media,for example, secondary storage devices such as hard disks, floppy disks,and CD-ROMs; or other forms of ROM or RAM either currently known orlater developed. The computer-readable storage media may benon-transitory computer-readable media, which includes CD-ROMs, volatileor non-volatile memory such as ROM and RAM, or any other suitablestorage device. As another example, the systems, components, and flowdiagrams illustrated herein include one or more components and/oroperations. Each system, component, or set of operations may includefewer, additional, or different components or operations. Components oroperations indicated as optional in the drawings may just be one exampleof components or operations that are optional. Components or operationsnot marked as optional may, in fact, be optional in some examples.

Furthermore, although specific components of innovations were described,methods, systems, and articles of manufacture consistent with theinnovation may include additional or different components. For example,a processor may be implemented as a microprocessor, microcontroller,application specific integrated circuit (ASIC), discrete logic, or acombination of other type of circuits or logic. Similarly, memories maybe DRAM, SRAM, Flash or any other type of memory. Flags, data,databases, tables, entities, and other data structures may be separatelystored and managed, may be incorporated into a single memory ordatabase, may be distributed, or may be logically and physicallyorganized in many different ways. The components may operateindependently or be part of a same program. The components may beresident on separate hardware, such as separate removable circuitboards, or share common hardware, such as a same memory and processorfor implementing instructions from the memory. Programs may be parts ofa single program, separate programs, or distributed across severalmemories and processors.

The respective logic, software or instructions for implementing theprocesses, methods and/or techniques discussed throughout thisdisclosure may be provided on computer-readable media or memories orother tangible media, such as a cache, buffer, RAM, removable media,hard drive, other computer readable storage media, or any other tangiblemedia or any combination thereof. The tangible media include varioustypes of volatile and nonvolatile storage media. The functions, acts ortasks illustrated in the figures or described herein may be executed inresponse to one or more sets of logic or instructions stored in or oncomputer readable media. The functions, acts or tasks are independent ofthe particular type of instructions set, storage media, processor orprocessing strategy and may be performed by software, hardware,integrated circuits, firmware, micro code, or any type of otherprocessor, operating alone or in combination. Likewise, processingstrategies may include multiprocessing, multitasking, parallelprocessing and/or any other processing strategy known now or laterdiscovered. In one embodiment, the instructions are stored on aremovable media device for reading by local or remote systems. In otherembodiments, the logic or instructions are stored in a remote locationfor transfer through a computer network or over telephone lines. In yetother embodiments, the logic or instructions are stored within a givencomputer, CPU, GPU, or system.

A second action may be said to be “in response to” a first actionindependent of whether the second action results directly or indirectlyfrom the first action. The second action may occur at a substantiallylater time than the first action and still be in response to the firstaction. Similarly, the second action may be said to be in response tothe first action even if intervening actions take place between thefirst action and the second action, and even if one or more of theintervening actions directly cause the second action to be performed.For example, a second action may be in response to a first action if thefirst action sets a flag and a third action later initiates the secondaction whenever the flag is set.

To clarify the use of and to hereby provide notice to the public, thephrases “at least one of <A>, <B>, . . . and <N>” or “at least one of<A>, <B>, . . . <N>, or combinations thereof” or “<A>, <B>, . . . and/or<N>” are defined by the Applicant in the broadest sense, superseding anyother implied definitions hereinbefore or hereinafter unless expresslyasserted by the Applicant to the contrary, to mean one or more elementsselected from the group comprising A, B, . . . and N. In other words,the phrases mean any combination of one or more of the elements A, B, .. . or N including any one element alone or the one element incombination with one or more of the other elements which may alsoinclude, in combination, additional elements not listed.

While various embodiments of the innovation have been described, it willbe apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible within the scope of theinnovation. Accordingly, the innovation is not to be restricted exceptin light of the attached claims and their equivalents.

What is claimed is:
 1. A non-transitory computer-readable storage mediumcomprising a plurality of instructions executable with a processor, theinstructions including: instructions executable to receive, at a firstclient device from a component in the first client device, a request toallocate a portion of memory, wherein a memory appliance and the firstclient device are on a network, and a region of memory of the memoryappliance is allocated as external memory prior to receipt of therequest to allocate the portion of memory at the first client device,wherein the external memory is external to the first client device and asecond client device, but is primary memory to the first client deviceand the second client device; instructions executable to select, at thefirst client device in coordination with the second client device and inresponse to the request to allocate the portion of memory, a subset ofthe region of memory of the memory appliance; and instructionsexecutable to map, at the first client device, at least the subset ofthe region of memory to a virtual address space, wherein data in theportion of the external memory is accessible from the first clientdevice via client-side memory access in which a communication interfaceof the memory appliance is configured to access the region of memory onthe memory appliance.
 2. The computer readable medium of claim 1,wherein selection of the subset of the region of memory in coordinationwith the second client device is based on a memory-allocation datastructure, wherein the memory-allocation data structure is shared withthe second client device.
 3. The computer readable medium of claim 2further comprising instructions executable to update thememory-allocation data structure to indicate that the portion has beenallocated as part of the selection of the subset of the region of memoryin coordination with the second client device.
 4. The computer readablemedium of claim 2, wherein the memory-allocation data structure isaccessible from the first client device and the second client device viaclient-side memory access.
 5. The computer readable medium of claim 2comprising instructions executable to access the memory-allocation datastructure atomically as part of the selection of the subset of theregion of memory in coordination with the second client device.
 6. Thecomputer readable medium of claim 2, wherein access to thememory-allocation data structure is coordinated based on one or moresynchronization primitives.
 7. The computer readable medium of claim 2,wherein the memory-allocation data structure is included in the regionof memory of the memory appliance.
 8. The computer readable medium ofclaim 2, wherein the memory-allocation data structure is included inmetadata associated with the region of memory.
 9. The computer readablemedium of claim 2, wherein the memory-allocation data structure includesone or more indicators that indicate whether corresponding portions ofthe region are allocated.
 10. The computer readable medium of claim 1,wherein selection of the subset of the region of memory in coordinationwith the second client device is based on message-passing between thefirst client and the second client.
 11. The computer readable medium ofclaim 1, wherein the at least the subset of the region of memory mappedto the virtual address space includes all of the region of memory andwherein the at least the subset of the region of memory is mapped to thevirtual address space before the request to allocate a portion of memoryis received and/or before the subset of the region of memory isselected.
 12. The computer readable medium of claim 1, wherein a secondsubset of the region of memory is allocable by the second client devicein response to a request to allocate a second portion of memory.
 13. Thecomputer readable medium of claim 1 further comprising instructionsexecutable to initialize at least a second portion of external memoryafter the at least the second portion of external memory is mapped atthe first client device.
 14. The computer readable medium of claim 1further comprising instructions executable to free the subset of theregion of memory in response to destruction of a correspondingapplication logic or to a determination that the correspondingapplication logic is destroyed.
 15. A method comprising: receiving, at afirst client device, a request to allocate a portion of memory, whereina memory appliance and the first client device are connected by anetwork, and a region of memory of the memory appliance is allocated asexternal memory before receipt of the request to allocate the portion ofmemory at the first client device; selecting, at the first client deviceand in coordination with a second client device on the network, a subsetof the region of memory for the portion of memory allocated, wherein theportion of memory allocated is external to the first client device butis primary memory to the first client device, wherein by coordinationwith the second client device, the subset of the region of memory isselected without the second client device having selected the samesubset of the region of memory for allocation as external memory for thesecond client device; and mapping, at the first client device, at leastthe subset of the region of memory to a virtual address space.
 16. Themethod of claim 15, wherein selecting the subset of the region of memoryin coordination with the second client comprises accessing amemory-allocation data structure that is shared by the first client andthe second client, the memory-allocation data structure indicating whichportions of the region of memory are allocated by a memory user of thefirst client.
 17. The method of claim 16, wherein selecting the subsetof the region of memory in coordination with the second client comprisesidentifying a free portion of the region of memory of the memoryappliance from the memory-allocation data structure shared by the firstclient and the second client.
 18. The method of claim 16 furthercomprising migrating an application logic from the first client deviceto the second client device by mapping, at the second client, theportion of the region of memory of the memory appliance that isindicated by the memory-allocation data structure to be allocated to theapplication logic on the first client.
 19. The method of claim 18,wherein migrating the application logic includes migrating theapplication logic from the first client device to the second clientdevice without copying any data of the allocated portion of memory fromthe first client device to the second client device.
 20. The method ofclaim 18 further comprising determining the portion of the region ofmemory of the memory appliance allocated to the application logic on thefirst client by accessing the memory-allocation data structure from thesecond client device.